bluuebunny/crossref_metadata_2025 huggingface dataset:
An investigation of cold cloud formation with a three‐dimensional model with explicit microphysics
Authors: Mavromatidis Elias , Kallos George
Published: July 2003

In the framework of the European Union‐funded project “Investigation of Cloud by Ground‐based and Airborne Radar and Lidar” (CARL) the Regional Atmospheric Modeling System (RAMS) was used in order to study ice crystal formation and evolution in a cold cloud formation during a field program over Palaiseau, France. Sensitivity tests were performed so as to bind the uncertainty from various factors controlling model results. Emphasis is given to the sensitivity of the model with respect to the shape parameter of gamma distribution in the cloud microphysics module. Sensitivity analysis of the model was also performed in relation to the initialization of the simulation. The results are compared to in situ and remote sensing observations of the cloud formation. The analysis revealed that the model was able to reproduce the cloud characteristics (e.g., the spatial and temporal variability of the phenomena and the cloud geometry) in a satisfactory way. A detailed comparison of the model results with aircraft data showed that the model‐calculated water content and number concentration deviate significantly for the small‐size particle bin (2–47 microns) but are in good agreement for the medium‐ (25–800 microns) and large‐size (200–6400 microns) bins. The differences for the smaller particles can partially be attributed to both poor performance of the microphysical algorithms and instrument inaccuracies. Some differences for the larger particles can be attributed either to the definition of the cloud boundaries by the model or to disturbances caused by the ascent path of the aircraft or both. The time of model initialization is also an important factor affecting cloud formation during the first few hours of the simulation. The performed simulations and model/data intercomparisons showed that RAMS is able to reproduce most of the microphysical parameters of cold cloud formations satisfactorily while utilizing conventional meteorological fields and observations for initial and boundary conditions.
Mineral Dust Entrainment and Deposition (DEAD) model: Description and 1990s dust climatology
Authors: Zender Charles S. , Bian Huisheng , Newman David
Published: July 2003

We describe a model for predicting the size‐resolved distribution of atmospheric dust for climate and chemistry‐related studies. The dust distribution from 1990 to 1999 is simulated with our mineral aerosol entrainment and deposition module embedded in a chemical transport model. Mobilization processes include entrainment thresholds for saltation, moisture inhibition, drag partitioning, and saltation feedback. For mobilization we assume that soil texture is globally uniform and is replete with saltators. Soil erodibility is prescribed by a new physically based geomorphic index that is proportional to the runoff area upstream of each source region. Dry deposition processes include sedimentation and turbulent mix‐out. Nucleation scavenging and size‐resolved washout in both stratiform and convective cloud types are represented. Simulations of the 1990s broadly agree with station observations and satellite‐inferred dust distributions. Without invoking anthropogenic mechanisms the model captures the seasonal migration of the transatlantic African dust plume, and it captures the spring maximum in Asian dust outflow and concentration over the Pacific. We estimate the 1990s global annual mean and variability of D < 10 μm dust to be the following: emissions, 1490 ± 160 Tg yr−1; burden, 17 ± 2 Tg; and optical depth at 0.63 μm, 0.030 ± 0.004. This emission, burden, and optical depth are significantly lower than some recent estimates. The model underestimates transport and deposition of East Asian and Australian dust to some regions of the Pacific Ocean. An underestimate of long‐range transport of particles larger than 3 μm contributes to this bias. Our experiments support the hypothesis that dust emission “hot spots” exist in regions where alluvial sediments have accumulated and may be disturbed.
Surface soil moisture monitoring over Europe using Special Sensor Microwave/Imager (SSM/I) imagery
Authors: De Ridder Koen
Published: July 2003

A methodology to infer skin soil moisture from time series of passive microwave imagery is presented. Based on temporal changes in the microwave polarization difference temperature, it yields a quantitative moisture estimate as a fraction of field capacity. Based on a processing technique that separates low‐frequency components caused by vegetation changes from fast precipitation‐induced changes, its main feature is the complete independence of ground‐based data. The method solely employs information contained in the microwave signal itself. When applied on Special Sensor Microwave/Imager imagery over the European continent, it is found that the methodology is only applicable to areas with sparse vegetation cover, where the fractional error (with respect to field capacity) is estimated to range from 16 to 28%. Finally, comparison of calculated moisture time series with observed precipitation shows a fair agreement.
Parameterization of cloud droplet formation in global climate models
Authors: Nenes Athanasios , Seinfeld John H.
Published: July 2003

An aerosol activation parameterization has been developed based on a generalized representation of aerosol size and composition within the framework of an ascending adiabatic parcel; this allows for parameterizing the activation of chemically complex aerosol with an arbitrary size distribution and mixing state. The new parameterization introduces the concept of “population splitting,” in which the cloud condensation nuclei (CCN) that form droplets are treated as two separate populations: those that have a size close to their critical diameter and those that do not. Explicit consideration of kinetic limitations on droplet growth is introduced. Our treatment of the activation process unravels much of its complexity. As a result of this, a substantial number of conditions of droplet formation can be treated completely free of empirical information or correlations; there are, however, some conditions of droplet activation for which an empirically derived correlation is utilized. Predictions of the parameterization are compared against extensive cloud parcel model simulations for a variety of aerosol activation conditions that cover a wide range of chemical variability and CCN concentrations. The parameterization tracks the parcel model simulations closely and robustly. The parameterization presented here is intended to allow for a comprehensive assessment of the aerosol indirect effect in general circulation models.
Determination of reflection coefficients at the top and bottom of elevated strike objects struck by lightning
Authors: Bermudez J. L. , Rubinstein M. , Rachidi F. , Heidler F. , Paolone M.
Published: July 2003

In this paper, we present an analysis of lightning return stroke currents along an elevated strike object. We derive closed form expressions, both in the frequency domain and in the time domain, to calculate the lightning current at any height along a strike object taking into account reflections at the top and at the bottom. The frequency dependence of reflection coefficients is taken into account. We also derive an expression to calculate the reflection coefficient as a function of frequency at the bottom of the lightning strike object from two currents measured at different heights along the strike object. We show that, if the current and its time derivative overlap with reflections at the top or bottom of the strike object, it is impossible to derive the reflection coefficient at the top of the strike object exactly from any number of simultaneous current measurements. We propose an extrapolation method to estimate this reflection coefficient. We propose a second method to calculate the top reflection coefficient from just one current derivative measurement if the current derivative and its reflections do not overlap significantly. We apply the proposed methodology to experimental data obtained on Peissenberg Tower (Germany) consisting of lightning currents measured at two heights. The results suggest that the reflection coefficient at ground level can be considered as practically constant in the frequency range 100 kHz to 800 kHz. Although the estimated ground and top reflection coefficients are in good overall agreement with values found in the literature, the estimated values for the top reflection coefficient from the extrapolation method are somewhat lower than those found employing the current derivative method; the differences are discussed.
Nitrous oxide flux to the atmosphere from the littoral zone of a boreal lake
Authors: Huttunen Jari T. , Juutinen Sari , Alm Jukka , Larmola Tuula , Hammar Taina , Silvola Jouko , Martikainen Pertti J.
Published: July 2003

The surface‐atmospheric exchange of nitrous oxide (N2O) was investigated in the vegetated littoral zone of a eutrophied midboreal lake (Lake Kevätön, Finland) with a static chamber technique. During a dry summer (three to six samplings per site), the meadow site and two marsh sites in the temporarily flooded eulittoral zone and the Phragmites australis‐dominated site in the continuously flooded infralittoral zone had mean daytime N2O‐N emissions from 11 ± 7 to 22 ± 7 μg m−2 h−1, whereas the Nuphar lutea‐dominated site in the infralittoral zone had a mean N2O flux close to zero. During a wet summer (13–14 samplings per site), the mean daytime N2O‐N fluxes ranged from 4 ± 1 to 15 ± 5 μg m−2 h−1 at the three eulittoral sites and were negligible at the two infralittoral sites. The littoral zone occupied 26% of the lake area but was estimated to account for most of the N2O emissions from the lake. The studied eulittoral zone, which did not have adjacent nitrogen fertilization, exhibited higher N2O emissions during the summer than seen in northern natural ecosystems in general, including peatlands, forests, and the pelagic regions of lakes. Thus in lake‐rich landscapes the littoral zone and other lake‐associated wetlands must be considered as potential sources of atmospheric N2O. An assessment of their atmospheric importance requires further data on the N2O fluxes and their regulation in different littoral areas and on the total littoral coverage, neither of which is yet available.
Ecosystem‐atmosphere exchange of carbon dioxide over a mixed hardwood forest in northern lower Michigan
Authors: Schmid H. P. , Su H.‐B. , Vogel C. S. , Curtis P. S.
Published: July 2003

We report results from the first 3 years (1999–2001) of long‐term measurements of net ecosystem exchange (NEE) at an AmeriFlux site over a mixed hardwood forest in northern lower Michigan. The primary measurement methodology uses eddy covariance systems with closed‐path infrared gas analyzers at two heights (46 and 34 m) above the forest (canopy height is ∼22 m). One objective is to contribute to a more firmly established methodology of estimating annual net ecosystem production (NEP), by systematically examining the consequences of several variations of criteria to identify periods of unreliable measurements, and to fill gaps in the data. We compared two methods to fill data gaps (about 30% of time in 1999) due to missing observations or rejected data after quality control; one using short‐term ensemble averages of the daily course and the other by semiempirical parametric models based on relationships between ecosystem respiration and soil temperature and between gross ecosystem photosynthetic uptake and photosynthetically active radiation. The modeled estimates were also used to replace eddy covariance fluxes during periods of weak and/or poorly developed turbulence when eddy covariance measurements cannot be expected to represent the ecosystem exchange. Examination of the fractions of eddy covariance fluxes and storage change relative to the expected ecosystem respiration suggested a friction velocity (u*) of 0.35 m s−1 as the lower limit for the acceptance of micrometeorologically determined NEE for this site. The differences in estimated annual NEP due to different criteria of data acceptance, measurement height, or gap‐filling strategies turned out to be at least as large as the interannual variations over the 3 years. After discussing various analysis strategies we conclude that the best estimate of annual NEP at our site is achieved by replacing data gaps and measurements in low‐u* conditions at all times with site and period‐specific parametric models, using the upper measurement level (about 2.1 canopy heights). These “best estimates” of annual NEP for 1999–2001 amounted to 170 (1999), 160 (2000), and 80 (2001) g C m−2. We also discuss some problems of assigning quantitative estimates of uncertainty for annual NEP.
Intercomparison of water and energy budgets for five Mississippi subbasins between ECMWF reanalysis (ERA‐40) and NASA Data Assimilation Office fvGCM for 1990–1999
Authors: Betts Alan K. , Ball John H. , Bosilovich Michael , Viterbo Pedro , Zhang Yuanchong , Rossow William B.
Published: July 2003

Using monthly means for 1990–1999, we assess the systematic biases in temperature and humidity and the surface energy and water budgets of both European Centre for Medium‐Range Weather Forecasts (ECMWF) 40‐year reanalysis (ERA‐40) and the of the NASA Data Assimilation Office atmospheric finite‐volume general circulation model (fvGCM) for five Mississippi subbasins. We compare ERA‐40 and the fvGCM with basin averages of surface observations of temperature, humidity and precipitation, the river basin estimates for the hydrological balance from Maurer et al. [2002], and the International Satellite Cloud Climatology Project (ISCCP) retrieved skin temperature and surface radiation fluxes. We show the role of the soil water analysis in ERA‐40, which generally supplies water in summer and removes it in winter and spring. The ERA‐40 snow analysis increments are a significant contribution to the (smaller) frozen water budget. Compared with National Climate Data Center (NCDC) observations of screen temperature, ERA‐40 generally has a relatively small (≤1 K) positive temperature bias in all seasons for the Mississippi basins, while the fvGCM has a large cold bias in temperature in winter. The ISCCP skin temperature estimate is generally high in winter and a little low in summer, compared to ERA‐40 and the NCDC screen level temperature. For the western basins, summer precipitation is high in the fvGCM, while for the eastern basins it is high in ERA‐40 (in 12–24 hour forecasts after spin‐up). Summer evaporation is higher in the fvGCM than in ERA‐40, while winter evaporation has a high bias in ERA‐40, leading to a corresponding high bias in specific humidity. Net shortwave radiation probably has a high bias in the fvGCM in summer. The seasonal cycle of incoming shortwave is much flatter in ERA‐40 than the ISCCP data, suggesting that the reanalysis may have too much reflective cloud in summer and too little in the cooler seasons. The temperature biases at the surface in both the fvGCM and the ISCCP data clearly have a negative impact on the surface long‐wave radiation fluxes, although the bias in the net long‐wave flux is rather less.
Data collection and management for Global Energy and Water Cycle Experiment (GEWEX) Continental‐Scale International Project (GCIP)
Authors: Leese J. , Williams S. , Jenne R. , Ritchie A.
Published: July 2003

The Global Energy and Water Cycle Experiment (GEWEX) Continental‐Scale International Project (GCIP) was focused on the Mississippi River basin to take advantage of the existing meteorological and hydrological networks that were upgraded with new Doppler radars, wind profilers, and automatic weather stations together with an upgraded version of the Geostationary Operational Environmental Satellites (GOES) operated by the United States. The Mississippi River basin encompasses a wide range of climate, soil moisture conditions, vegetation types, and surface topography. The GCIP Science Plan identified the major phase of GCIP as the 5‐year Enhanced Observing Period (EOP), targeted for 1995 to 2000, during which original data sets would be assembled for the GCIP database. GCIP organized these data into in situ, model output and satellite remote sensing data. Data from three mesoscale models were included with the start dates ranging from May 1995 to April 1997. A number of GCIP Initial Data Sets (GIDS) were prepared, starting in 1993, to provide the data services support during the buildup period before the 5‐year EOP. The data sets were compiled for on‐line access by GCIP investigators and were also published on CD‐ROM. A number of special data sets, in addition to the EOP data sets, were compiled during the course of GCIP. Some of the most significant special data sets are summarized in this paper.
Physical, chemical, and ultraviolet radiative characteristics of aerosol in central Alaska
Authors: Wetzel Melanie A. , Shaw Glenn E. , Slusser James R. , Borys Randolph D. , Cahill Catherine F.
Published: July 2003

A new long‐term monitoring site for providing multiwavelength (ultraviolet through near‐infrared) and broadband irradiances has been established at the Poker Flat Research Range, Alaska, in order to assess the impacts of ozone, cloud cover, surface albedo, and aerosol conditions on trends in ultraviolet (UV) radiation reaching the surface. Targeted field measurements were conducted in the first year of site operation to characterize the properties of aerosols commonly found in the study region. Chemical analysis was used to match aerosol composition to aerosol size distributions and spectral aerosol optical depth (AOD). Results are reported on four air mass types: three springtime examples, including an Asian air mass with Gobi Desert dust, aged industrial pollution from the Arctic, and humid marine air, and a comparative case in late summer. Aerosol imported to central Alaska from extraregional sources produced small to moderate increases in UV optical depth calculated from direct‐beam spectral extinction and a limited reduction in transmittance at UV wavelengths. Marine aerosol in a high‐humidity environment produced the largest impact on UV extinction. The Angstrom coefficients and single scattering albedos calculated from the spectral AOD and irradiances and the spectral characteristics of size‐specific aerosol absorption measurements showed distinct differences between the aerosol source types, suggesting that even in cases of low aerosol concentration, air mass characteristics influence the spectral and angular distributions of UV radiation that are important for modeling photochemical processes and biological exposure.
Estimates of cloud vertical structure and water amount over tropical oceans using VIRS and TMI data
Authors: Ho Shu‐peng , Lin Bing , Minnis Patrick , Fan Tai‐Fang
Published: July 2003

A microwave, visible and infrared (MVI) method was applied to coincident, collocated Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and VIRS (Visible and Infrared Scanner) data collected from January to August 1998 to estimate the cloud vertical structure and water path over tropical oceans. The derived quantities include the liquid water path (LWP), ice water path (IWP), total water path (WP), the frequencies of single‐layer and overlapping nonprecipitating clouds, and the cloud top‐height, base‐height and thickness for single‐layered water clouds. LWP data retrieved from TMI measurements were compared with global and regional LWP retrieved from VIRS for warm nonprecipitating clouds for different seasons. The global mean difference between TMI LWP and VIRS LWP is less than 0.01 mm and varies with season. For cold clouds, the TMI LWP is only 25–30% of the VIRS WP. In these cases, the ice clouds observed by VIRS overlap liquid water clouds. This result is similar to that from an earlier study, however, the well‐matched TMI and VIRS data provide more accurate instantaneous estimates than were previously possible. The assumption, that the cloud is entirely ice, used to compute IWP introduces some errors in the WP because of cloud overlapping. However, the difference between IWP estimated for all TMI FOVs containing only ice‐phase VIRS pixels and the IWP estimated from the difference between the VIRS WP and TMI LWP is less than 10%. This result suggests that IWP is independent of the lower‐level clouds for nonprecipitating systems. For warm single‐layered clouds, the estimated low‐cloud‐base altitudes (∼800m) and thicknesses (between 800 m to 1000 m) are, on average, very close to low‐cloud results derived from combined surface and upper‐air observations. The frequency of overlapped nonprecipitating clouds over ocean was about 4%, 16% and 38% for low, middle, and high clouds, respectively. The results clearly demonstrate the potential for enhanced monitoring of maritime clouds using infrared, solar, and microwave imagers on the same platform.
Mars Surveyor Program '01 Mars Environmental Compatibility Assessment wet chemistry lab: A sensor array for chemical analysis of the Martian soil
Authors: Kounaves Samuel P. , Lukow Stefan R. , Comeau Brian P. , Hecht Michael H. , Grannan‐Feldman Sabrina M. , Manatt Ken , West Steven J. , Wen Xiaowen , Frant Martin , Gillette Tim
Published: July 2003

The Mars Environmental Compatibility Assessment (MECA) instrument was designed, built, and flight qualified for the now canceled MSP (Mars Surveyor Program) '01 Lander. The MECA package consisted of a microscope, electrometer, material patch plates, and a wet chemistry laboratory (WCL). The primary goal of MECA was to analyze the Martian soil (regolith) for possible hazards to future astronauts and to provide a better understanding of Martian regolith geochemistry. The purpose of the WCL was to analyze for a range of soluble ionic chemical species and electrochemical parameters. The heart of the WCL was a sensor array of electrochemically based ion‐selective electrodes (ISE). After 20 months storage at −23°C and subsequent extended freeze/thawing cycles, WCL sensors were evaluated to determine both their physical durability and analytical responses. A fractional factorial calibration of the sensors was used to obtain slope, intercept, and all necessary selectivity coefficients simultaneously for selected ISEs. This calibration was used to model five cation and three anion sensors. These data were subsequently used to determine concentrations of several ions in two soil leachate simulants (based on terrestrial seawater and hypothesized Mars brine) and four actual soil samples. The WCL results were compared to simulant and soil samples using ion chromatography and inductively coupled plasma optical emission spectroscopy. The results showed that flight qualification and prolonged low‐temperature storage conditions had minimal effects on the sensors. In addition, the analytical optimization method provided quantitative and qualitative data that could be used to accurately identify the chemical composition of the simulants and soils. The WCL has the ability to provide data that can be used to “read” the chemical, geological, and climatic history of Mars, as well as the potential habitability of its regolith.
Last glacial sea surface temperatures and sea‐ice extent in the Southern Ocean (Atlantic‐Indian sector): A multiproxy approach
Authors: Gersonde R. , Abelmann A. , Brathauer U. , Becquey S. , Bianchi C. , Cortese G. , Grobe H. , Kuhn G. , Niebler H.‐S. , Segl M. , Sieger R. , Zielinski U. , Fütterer D. K.
Published: July 2003

On the basis of the quantitative study of diatom, radiolarian, and planktic foraminiferal assemblages, we estimated summer sea surface temperature (SSST) and sea‐ice extent at 50 sediment core localities in the Atlantic and western Indian sector of the Southern Ocean to reconstruct the last glacial environment at the GLAMAP (18 to 15 ka, equal to 21,500 to 18,000 calendar (cal) years BP) and EPILOG (19.5 to 16.0 ka, equal to 23,000 to 19,000 cal years BP) time slices. Stratigraphic identification of the time slices was accomplished by a combination of AMS 14C measurements, benthic isotope, and siliceous microfossil abundance records. While the SSST estimates reveal greater surface water cooling than reconstructed by CLIMAP [1981], reaching a maximum in the area of the present Subantarctic Zone, the sea‐ice reconstruction indicates that CLIMAP overestimated the expansion of the Antarctic sea‐ice field, especially for austral summer. During winter the sea‐ice field was expanded by 60–70% compared to the present. Last glacial summer sea surface isotherms indicate a northward shift of the zonal bands of the Antarctic Circumpolar Current and a relative expansion of the cold water realm south of the Subantarctic Front by ∼5° in latitude. This coincides with a northward displacement of the zone of enhanced biogenic silica deposition and iceberg occurrence. As a result of northward expansion of Antarctic cold waters and a relatively small displacement of the Subtropical Front, thermal gradients were steepened during the last glacial in the area of the present Subtropical Front. The northward displacement of Antarctic cold waters and the related deflection of Southern Ocean waters along the eastern boundary of South America may have resulted in a weakened “cold water route” across the Drake Passage. In contrast, the transport of warm and salty surface water from the Indian into the Atlantic Ocean via the “warm water route” was not blocked allowing continuous but reduced import of heat into the South Atlantic.
Is methane venting at the seafloor recorded by δ13C of benthic foraminifera shells?
Authors: Torres M. E. , Mix A. C. , Kinports K. , Haley B. , Klinkhammer G. P. , McManus J. , de Angelis M. A.
Published: July 2003

The isotopic composition of the dissolved inorganic carbon (DIC) collected at sites of active methane discharge on Hydrate Ridge, Oregon, reveals anaerobic methane oxidation mediated by bacteria, with δ13CDIC reaching values as low as −48‰ in the upper 4 cm of the sediment. In spite of the high sulfide levels in the discharging fluids, living specimens of the benthic foraminifera Uvigerina peregrina are abundant in the vents, probably owing to the rich bacterial food source. Although pore water δ13CDIC is extremely low (−6 to −48‰), the δ13C values of living (Rose Bengal stained) foraminifera shells collected from active methane seeps are not significantly lower than those observed in nonventing pelagic sediments, and are within the range expected from local organic matter decomposition (0 to −4‰). The apparent δ13C disequilibrium between biogenic calcite and DIC suggests that at seep localities, foraminifera calcify mostly during periods when there is little methane discharge or during intermittent episodes of seawater flow into the sediments. The isotopic composition and Mg/Ca ratios of fossil (unstained) foraminifera recovered at carbonate‐rich sites on the northern Hydrate Ridge reveals overprinting of the biogenic record by inorganic calcite with high Mg/Ca and anomalously low δ13C values. Thus overprinting of the original isotopic composition of foraminifera by overgrowths or recrystallization at or below the sediment surface, rather than primary calcification in contact with 13C depleted DIC, can explain extreme 13C depletion observed in fossil foraminifera recovered from sites of active methane discharge.
Noise maps in aperture synthesis radiometric images due to cross‐correlation of visibility noise
Authors: Butora Robert , Camps Adriano
Published: July 2003

This study deals with the calculation of the distribution of radiometric errors (“noise maps”) in the images formed by a two‐dimensional aperture synthesis radiometer, specifically the MIRAS and the HUT‐2D instruments. MIRAS is a spaceborne Y‐shaped interferometric radiometer that will be boarded in the European Space Agency's SMOS Earth Explorer Mission. The HUT‐2D is a U‐shaped airborne interferometric radiometer under development by the Helsinki University of Technology. The study focuses on the known fact that the cross‐correlation of the visibility noise does depend on the shape of the sensor. We investigate this dependence for the Y and the U configurations, taking into account also the results of previous studies on redundancy and tapering.
The Mw 7.5 1999 Ambrym earthquake, Vanuatu: A back arc intraplate thrust event
Authors: Regnier Marc , Calmant Stéphane , Pelletier Bernard , Lagabrielle Yves , Cabioch Guy
Published: July 2003

On 26 November 1999, a Mw 7.5 thrust earthquake occurred in the Vanuatu back arc seismic zone. The aftershocks seismicity defines a west dipping plane down to a depth of 20 km consistent with the focal mechanism geometry. The shallow focal depth of the main shock and the coincidence of the surface projection of the plane of aftershocks with a 600 m high sea bottom fault scarp indicate the fault plane ruptured up to the surface. The size of the fault has been estimated to 50 × 25 km2 from the aftershocks distribution and modeling of coseismic vertical motion inferred from biological markers. The inferred length indicates the rupture affected the whole Ambrym segment, but inversion of GPS horizontal displacement data indicates most of the seismic moment has been released on a smaller 35 × 20 km2 fault surface with an average slip of 6.5 m. Foreshock and aftershock seismicity are organized in planar seismic zones parallel to the inferred main shock rupture plane. This spatiotemporal distribution of imaged fault suggests that the thrust front propagates in times by eastward jumps to new intraplate faults occurring in the western edge of the North Fiji Basin. The back arc present setting could eventually represent the very early stages of an incipient subduction zone with reverse polarity. The intraplate fault model yields shortening by thickening of the back arc crust. Using crustal balanced sections to model the deformations over the last 1.8 m.y. period, a maximum shortening of 55 km has been found
Gully erosion and sediment production: Te Weraroa Stream, New Zealand
Authors: Gomez Basil , Banbury Kate , Marden Mike , Trustrum Noel A. , Peacock David H. , Hoskin Peter J.
Published: July 2003

We derive a sediment budget for Te Weraroa Stream, New Zealand, the principal drainage in a small (29 km2) steepland catchment where gully erosion, triggered by conversion to pasture early in the twentieth century, was ameliorated by reforestation that commenced in 1962. Estimates of sediment production were made using the change in gully area observed in sequential aerial photographs. Channel storage was assessed from stream cross‐section surveys. At its peak, gully erosion affected ∼6% of the total catchment area. The amount of sediment contributed from gullies declined by 62% as the forest became established, but of the 28.7 Mt of sediment generated by gully erosion between 1950 and 1988, 48% was stored in the channel along the lower 8 km of Te Weraroa Stream. Even if the amount of sediment generated by gully erosion continues to decline, it likely will be many decades before the gravel is released from storage.
Aerosol absorption over the clear‐sky oceans deduced from POLDER‐1 and AERONET observations
Authors: Bellouin N. , Boucher O. , Tanré D. , Dubovik O.
Published: July 2003

We estimate aerosol absorption over the clear‐sky oceans using aerosol geophysical products from POLDER‐1 space measurements and absorption properties from ground‐based AERONET measurements. Our best estimate is 2.5 Wm−2 averaged over the 8‐month lifetime of POLDER‐1. Low and high absorption estimates are 2.2 and 3.1 Wm−2 based on the variability in aerosol single‐scattering albedo observed by AERONET. Main sources of uncertainties are the discrimation of the aerosol type from satellite measurements, and potential clear‐sky bias induced by the cloud‐screening procedure.
Whistler‐mode excitation and electron scattering during an interchange event near Io
Authors: Xiao F. , Thorne R. M. , Gurnett D. A. , Williams D. J.
Published: July 2003

The enhanced growth rate of whistler‐mode waves has been evaluated during an extended interchange event in the Io torus that occurred between 1709–1715 UT, on December 7, 1995. The energetic electron population observed by the Galileo EPD instrument is modeled using a bi‐loss‐cone distribution function (composed of a highly anisotropic component and a quasi‐isotropic component). During the injection event, the path integrated gain increases by more than a factor of ten over a broad frequency range near a few tenths of the electron gyrofrequency, consistent with the observed enhancement in Galileo PWS emissions. The enhanced PWS emissions are mainly associated with an increase in the flux of cyclotron resonant electrons below 55 keV. Scattering of electrons by the enhanced whistler‐modes causes the pitch‐angle distribution of resonant electrons to evolve from a normal “pancake” distribution in the unperturbed torus to a quasi‐isotropic distribution during the interchange event. This change provides an enhanced flux of electrons with mirror points close to Jupiter, which could be important for understanding the enhancement of Jovian auroral emissions in association with electron injection events.
A new snowfall detection algorithm over land using measurements from the Advanced Microwave Sounding Unit (AMSU)
Authors: Kongoli Cezar , Pellegrino Paul , Ferraro Ralph R. , Grody Norman C. , Meng Huan
Published: July 2003

This study introduces a new snowfall detection algorithm over land using AMSU measurements. The algorithm utilizes a combination of channels in the microwave window, water vapor and oxygen absorption regions. The new algorithm is combined with the current NOAA operational AMSU rain rate product for falling snow and rain areal extent retrievals over the U.S. These retrievals are compared with NEXRAD radar precipitation and local meteorological observations. Preliminary results demonstrate that the algorithm is robust in capturing winter precipitation with minimum classification errors.
Estimation of thermal structure in the mantle wedge of northeastern Japan from seismic attenuation data
Authors: Nakajima Junichi , Hasegawa Akira
Published: July 2003

We estimated thermal structure in the mantle wedge of NE Japan by applying the experimental results of olivine‐dominated rocks to seismic attenuation data. Obtained temperatures at a 40 km depth are 1000–1130°C and 960–1090°C beneath the volcanic front and the back‐arc side, respectively. We cannot obtain the areas with a temperature higher than 1400°C in the mantle wedge, which have been inferred from petrological studies. This is perhaps due to the localization of such anomalous areas. The obtained temperature is higher than that of the wet solidus of peridotite in the greater part of the back‐arc side, which suggests that the addition of aqueous fluids plays an important role in generating melts in the mantle wedge.
Numerical simulation of tsunami generation by pryoclastic flow at Aniakchak Volcano, Alaska
Authors: Waythomas Christopher F. , Watts Philip
Published: July 2003

Pyroclastic flows entering the sea are plausible mechanisms for tsunami generation at volcanic island arcs worldwide. We evaluate tsunami generation by pyroclastic flow using an example from Aniakchak volcano in Alaska where evidence for tsunami inundation coincident with a major, caldera‐forming eruption of the volcano ca. 3.5 ka has been described. Using a numerical model, we simulate the tsunami and compare the results to field estimates of tsunami run up.
Recovering permanent displacements from seismic records of the June 9, 1994 Bolivia deep earthquake
Authors: Zhu Lupei
Published: July 2003

Ground displacements of the 1994 deep Bolivia earthquake are recovered from six on‐scale velocity records of a temporary array located ∼600 km south of the epicenter. I first removed the instrument (STS‐2) response using a time‐domain deconvolution. To correct for baseline drift in the deconvolutions, I used two separate windows of the trace, one before and one after the transient motion from the earthquake, and fit them simultaneously with a 4th‐order polynomial. The amount of permanent displacement is included in the post‐transient signal window and is determined together with the polynomial coefficients by a least‐squares inversion. The polynomial is then subtracted from the displacement to remove the drift. I found that this technique produces robust displacement waveforms, as demonstrated by similar results at all stations. The obtained vertical permanent subsidences range from 5.5 to 6.4 mm, which agree well with predictions by using normal mode summation.
High altitude Himalayan climate inferred from glacial ice flux
Authors: Harper Joel T. , Humphrey Neil F.
Published: July 2003

Glaciological processes are modeled to investigate precipitation patterns and the resulting mass flux of snow and ice across Himalayan topography. Our model tracks the accumulation and ablation of snow and ice and the transport of snow and ice across the topography by glacier motion. We investigate high elevation precipitation on the Annapurna Massif by comparing the existing ice cover with model‐simulated glaciers produced by a suite of different precipitation scenarios. Our results suggest that precipitation reaches a maximum level well below the elevation of the highest peaks. Further, essentially no snow accumulates on the topography above an elevation of 6200–6300 m. Hence, the upper 1000+ m of the massif is a high elevation desert with little flux of snow and ice. Active glaciers are limited to a band of intermediate elevations where a maximum of about 60% of the landscape is covered by moving ice.
Towards understanding magnetic holes: Hybrid simulations
Authors: Baumgärtel K. , Sauer K. , Dubinin E.
Published: July 2003

One‐dimensional hybrid code simulations are presented which show that magnetic field depletions of variable length and depht can be maintained over long time in mirror‐stable high‐β plasmas under certain conditions while magnetic compressions cannot. This suggests that short‐scale magnetic holes (MHs), frequently observed in space plasmas, may be a feature of an essentially isotropic rather than a mirror‐unstable plasma. This suggestion is supported by additional simulations in anisotropic plasmas which reveal that localized magnetic depressions are not a typical feature of saturated states of the mirror instability.
Penetration of anthropogenic carbon into organic particles of the deep ocean
Authors: Druffel Ellen R. M. , Bauer James E. , Griffin Sheila , Hwang Jeomshik
Published: July 2003

In the late 1980s, bomb 14C was present in suspended particulate organic carbon (POC) from the North Central Pacific (NCP) and Sargasso Sea (SS) throughout most of the water column, demonstrating that deep POC had exchanged with atmospheric CO2 in the past 30 years. Upon reoccupation of these sites in 1999 and 2000, respectively, we observed that the δ13C values of suspended POC were lower than those measured a decade earlier. This demonstrates that anthropogenic CO2 from fossil fuel and biomass burning has penetrated a major organic matter pool in the deep ocean. Δ14C measured in the suspended POC showed similar or higher values in the deep Sargasso Sea and decreased values in the deep NCP compared to those measured previously. We use a box model to show that the differences in the radiocarbon results are likely due to the presence of resuspended sediment that is laterally advected from the continental margin to the deep Sargasso Sea.
A test of cirrus ice crystal scattering phase functions
Authors: Field P. R. , Baran A. J. , Kaye P. H. , Hirst E. , Greenaway R.
Published: July 2003

In‐situ ice crystal scattering has been measured in cirrus cloud with the Small Ice Detector laser scattering probe. Using light scattered from single particles (maximum dimension ∼<100 μm) at 4–10° and 20–40° we have tested ice crystal scattering phase functions for spheres, hexagonal columns, hexagonal plates, polycrystals an aggregate of columns and an analytic function. We find that phase functions that lack a pronounced 22° halo are the best representatives for the example data presented here. Spherical ice particle phase functions do not satisfy the measurements.
Anomalous Southward Advection During 2002 in the Northern California Current: Evidence from Lagrangian Surface Drifters
Authors: Barth John A.
Published: July 2003

Equatorward velocities in the upwelling jet of the northern California Current were 0.05–0.06 m s−1 faster in spring and summer 2002 than on average over 1998–2002. This result is based on a five‐year data set of surface drifters released across the continental margin off central Oregon (44.65°N) during April and July of each year. At this speed, anomalous water displacements of over a degree of latitude can occur in 20–25 days. Given a source of cold, Subarctic water to the north, this anomalous southward displacement is a plausible explanation for the cold, nutrient‐rich halocline water observed off Oregon during the summer of 2002. This interannual variability in the northern California Current and its implications for the ecosystem response, i.e., increased primary productivity, may be contrasted with interannual variability of the opposite sign ‐ increased poleward velocity, warmer temperatures and decreased productivity ‐ observed in this same region during El Niño years.
Decomposition of surface drifter observations in the Atlantic Ocean
Authors: Lumpkin Rick
Published: July 2003

Surface drifter observations are decomposed into mean, seasonal (annual and semiannual) and eddy components via Gauss‐Markov estimation. This approach helps separate seasonal fluctuations and mean values in the observationally‐sparse tropical and South Atlantic, where monthly mean values cannot be calculated at the spatial scale of the major currents. In some regions, large differences are found between these means and those obtained by simple binned averaging. The differences are attributed to inhomogeneous sampling of seasonal variability, and to the inherent bias of Lagrangian observations towards periods of low velocity. The analysis reveals strong seasonal variations of some surface currents, including a significant late spring reversal of the western North Equatorial Counter‐Current.
Air‐sea interaction at an oceanic front: Implications for frontogenesis and primary production
Authors: Chen Dake , Liu W. Timothy , Tang Wenqing , Wang Zhiren
Published: July 2003

Based on recent satellite observations, we hypothesize that there exists a significant air‐sea interaction at the shelf‐break front in the East China Sea. An idealized ocean‐atmosphere coupled model was designed to test this hypothesis and to study the physical processes involved in such an interaction, with emphasis on the oceanic part. A positive feedback between ocean and atmosphere was identified in the model and its consequences were evaluated. We found that air‐sea interaction, when combined with sloping topography, could provide a mechanism for the genesis of the shelf‐break front. The resulting frontal circulation and vertical mixing could bring nutrient‐rich subsurface water into the surface euphotic zone, thus making the frontal region a conspicuous place for primary production.
Long distance transport of pollen to Greenland
Authors: Rousseau Denis‐Didier , Duzer Danielle , Cambon Geneviève , Jolly Dominique , Poulsen Ulrik , Ferrier Jackie , Schevin Patrick , Gros Robert
Published: July 2003

Four pollen traps were recently placed at coastal sites in East and West Greenland in order to assess long distance transport of pollen to the Arctic domain. By identifying potential vegetation source areas associated with air mass pathways we were able to produce the first detailed record of pollen transport from eastern North America to Narsarsuaq, southern Greenland. The record is based on observations and on a transport and dispersion model used to calculate back trajectories of the air masses. The evidence points to the pollen being transported northward by the air mass over Newfoundland and the Labrador Sea before reaching Narsarsuaq. At this point, the air mass was at an altitude of 3000 m. Deposition of pollen grains occurred with downward air movements associated with a 0.5 mm/h rain. The source areas for these pollen grains differ from those of dust and certain other aerosols that reach the summit of the Greenland Ice Sheet. The results demonstrate the need for continued maintenance and analysis of the Greenland pollen trap data in order to improve our understanding of atmospheric circulation and transport to high northern latitudes.
Geophysical images of the Dead Sea Transform in Jordan reveal an impermeable barrier for fluid flow
Authors: Ritter O. , Ryberg T. , Weckmann U. , Hoffmann‐Rothe A. , Abueladas A. , Garfunkel Z. ,   DESERT Research Group
Published: July 2003

High‐resolutionseismictomography and magneto‐telluric (MT) soundings of the shallow crust show strong changes in material properties across the Dead Sea Transform Fault (DST) in the Arava valley in Jordan. 2D inversion results of the MT data indicate that the DST is associated with a strong lateral conductivity contrast of a highly conductive layer at a depth of approximately 1.5 km cut‐off at a position coinciding with the surface trace of the DST. At the same location, we observe a sharp increase of P wave velocities from <4 km/s west of the fault to >5 km/s to the east. The high velocities in the east probably reflect Precambrian rocks while the high electrical conductivity west of the DST is attributed to saline fluids within the sedimentary filling. In this sense, the DST appears to act as an impermeable barrier between two different rock formations. Such a localized fluid barrier is consistent with models of fault zone evolution but has so far not been imaged by geophysical methods. The situation at the DST is remarkably different from active segments of the San Andreas Fault which typically show a conductive fault core acting as a fluid conduit.
Comparison of TRMM rainfall retrievals with rain gauge data from the TAO/TRITON buoy array
Authors: Bowman Kenneth P. , Phillips Amy B. , North Gerald R.
Published: July 2003

Long‐term mean rainfall rates from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Precipitation Radar (PR) are compared with in situ measurements by rain gauges on the NOAA TAO/TRITON buoy array in the tropical Pacific. The buoy rain gauges have an advantage over most of the available ground truth data in that they are not influenced by the local meteorological effects of islands. Instantaneous TRMM retrievals averaged over 1° × 1° longitude‐latitude boxes are matched with 12‐hour‐averaged buoy rain amounts centered on the TRMM overpasses. The TMI has near‐zero bias with respect to the gauges when compared across climatologically different gauge locations (dry to wet). The PR is biased about 30% low relative to the gauges. These results are consistent with other ground truth studies and the known biases between the TMI and PR in the TRMM version 5 algorithms. Because rain gauges are thought to underestimate rainfall during windy conditions, further study of gauge biases would be useful.
Behavior of GPS‐derived precipitable water vapor in the mountain lee after the passage of a cold front
Authors: Okamura Osamu , Kimura Fujio
Published: July 2003

A mesoscale precipitation system generated half a day after a cold front passed over the Kanto Plain in the lee of the Chubu Mountains, Japan. The behavior of precipitable water vapor (PWV) associated with this precipitation system was investigated by the use of a dense Global Positioning System (GPS) network. After the passage of the cold front, a high‐level PWV zone was persistently observed over the Kanto Plain. The mesoscale precipitation system was induced in this zone. A numerical study indicated that the orographic effects on the prevailing wind are very important for sustaining the high‐level PWV zone over the Kanto Plain.