bluuebunny/crossref_metadata_2025 huggingface dataset:
Variations in ambient light emission from black smokers and flange pools on the Juan De Fuca Ridge
Authors: White S. N. , Chave A. D. , Reynolds G. T. , Gaidos E. J. , Tyson J. A. , Van Dover C. L.
Published: September 2002

Ambient light emitted by high‐temperature black smokers and flange pools on the Juan de Fuca Ridge was imaged using a new spectral imaging camera. Most of the light is emitted at long wavelengths (700–1000 nm) and corresponds well to thermal radiation from a body at the same temperature as the vents/flanges. However, black smokers also emit time‐varying radiation in the visible region (400–650 nm) which cannot be explained by a thermal source. This visible radiation is 1–2 orders of magnitude greater than would be expected for purely thermal radiation; it exhibits variation with time, despite relatively constant vent temperatures; and it is not associated with the hottest part of the plume (i.e. the orifice). Flange pools do not exhibit excess visible light over that for a thermal source, suggesting that the light at smokers is caused by mechanisms related to turbulence, mixing, or precipitation.
On the dome effect of Eppley pyrgeometers and pyranometers
Authors: Ji Qiang , Tsay Si‐Chee
Published: September 2002

Pyrgeometers and Pyranometers are fundamental instruments widely used for quantifying atmosphere‐surface energetics in climate studies. The dome effect of these instruments can cause a measurement uncertainty larger than 10 W m−2. Based on careful analysis, the dome factors of our two new pyrgeometers are found to lie in the range between 1.1 and 2.0. These values are far smaller than the value of 4.0 suggested by the World Meteorological Organization. The laboratory‐determined dome factors fall within this range, if pyrgeometers approach equilibrium with the blackbody target during calibration cycles. From recent field campaigns, consistent results for the dome factors are also obtained by analyzing nighttime pyrgeometer measurements, which were regarded as approaching equilibrium state. Furthermore, we utilized an energy balance equation to describe the thermal dome effect of pyranometers that is commonly referred to as the nighttime negative outputs or the dark‐offset. Lacking direct measurements of the dome and case temperatures of pyranometer, we used measurements from a pyrgeometer to derive and to account for the thermal dome effect of collocated pyranometers. This approximation revealed a reasonable agreement between calculations and measurements.
A regime view of northern hemisphere atmospheric variability and change under global warming
Authors: Monahan A. H. , Fyfe J. C. , Flato G. M.
Published: September 2002

The leading mode of wintertime variability in Northern Hemisphere sea level pressure (SLP) is the Arctic Oscillation (AO). It is usually obtained using linear principal component analysis, which produces the optimal, although somewhat restrictive, linear approximation to the SLP data. Here we use a recently introduced nonlinear principal component analysis to find the optimal nonlinear approximation to SLP data produced by a 1001 year integration of the CCCma coupled general circulation model (CGCM1). This approximation's associated time series is strongly bimodal and partitions the data into two distinct regimes. The first and more persistent regime describes a standing oscillation whose signature in the mid‐troposphere is alternating amplification and attenuation of the climatological ridge over Northern Europe, with associated decreasing and increasing daily variance over Northern Eurasia. The second and more episodic regime describes a split‐flow south of Greenland with much enhanced daily variance in the Arctic. In a 500 year integration with atmospheric CO2 stabilized at concentrations projected for year 2100, the occupation statistics of these preferred modes of variability change, such that the episodic split‐flow regime occurs less frequently while the standing oscillation regime occurs more frequently.
Uptake of acetone into sulfuric‐acid solutions
Authors: Imamura Takashi , Akiyoshi Hideharu
Published: September 2002

A time‐dependent uptake of acetone into sulfuric‐acid solutions was observed by means of a wetted‐wall flow reactor coupled to a photoionization mass spectrometer. The uptake was found to be reversible, and no reactive loss of acetone was observed. Henry's law constants of acetone into sulfuric‐acid were obtained from the time‐dependent uptake behavior observed for 50–79 wt% of H2SO4 solution at temperatures between 230 – 270 K. It was found that the solubility of acetone was mainly governed by its protonation in the acid. The observed Henry's law constant would unlikely be high enough to remove acetone efficiently from the gas phase in the upper troposphere; in addition, the reaction probability due to a sulfate‐mediated condensation was found to be too low.
The uptake of SO2 on synthetic sea salt and some of its components
Authors: Gebel Michael E. , Finlayson‐Pitts Barbara J. , Ganske Jane A.
Published: September 2002

The uptake of sulfur dioxide (SO2) on synthetic sea salt (SSS) and its components, NaCl and MgCl2•6H2O, was studied at 298 K using a Knudsen cell interfaced to a quadrupole mass spectrometer. Significant uptake on dried salts was not observed, placing upper limits on the uptake coefficients, γ, of < 1 × 10−4 for NaCl, < 5 × 10−4 for MgCl2•6H2O, and < 8 × 10−5 for SSS. However, SSS and MgCl2•6H2O that had not been dried before use showed significant uptake of SO2. The magnitude of the uptake depended strongly on the exposure time and the amount of water desorbing. Initially, the measured uptake coefficients for SO2 on SSS were as high as 0.09, but they rapidly decreased below 10−2 with a t−1/2 dependence as expected for approach to the equilibrium saturation concentration in an aqueous solution. The decreasing uptake coefficient slowly approaches zero over hours, consistent with reactions in a water layer with species such as CaCO3. The products of the reaction were shown by diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) to include low solubility metal sulfites. These studies show that uptake of SO2 on sea salt particles, even below their deliquescence/effluorescence points, can be treated as if it is into an aqueous salt solution.
De‐aliasing of global high frequency barotropic motions in altimeter observations
Authors: Stammer Detlef , Wunsch Carl , Ponte Rui M.
Published: September 2002

The existence of high frequency (periods shorter than 10 days) energetic barotropic motions in the ocean is shown to lead to a large aliasing error in satellite altimetric observations. This error is most easily seen in the “trackiness” of 10‐day altimetric maps, and commonly attributed to orbit error. Fortunately, existing ocean general circulation models, when driven with twice‐daily windstress fields, have considerable skill in predicting these motions. With improved forcing and models we can expect that in the future the alias can be largely suppressed by subtracting the model‐generated high frequency fields.
Impact of the North American ice‐sheet orography on the Last Glacial Maximum eddies and snowfall
Authors: Kageyama Masa , Valdes Paul J.
Published: September 2002

The present work evaluates the influence of the North American ice‐sheet orography on the Last Glacial Maximum (LGM, 21,000 years ago) atmospheric circulation and snowfall in the northern mid‐latitudes, focusing on the North Atlantic sector. Three Atmospheric General Circulation Model experiments are analysed: a control and an LGM climate simulation, and an LGM run with “flat” ice‐sheets over northern North America. This ice‐sheet orography affects lee‐cyclogenesis over North America and forces differences in stationary waves and therefore in the baroclinicity of the mean flow. As a result, the Atlantic storm‐track is reinforced in the “flat ice‐sheet” experiment compared to the LGM one. This, in turn, has a profound impact on snowfall over northern Europe, implying a coupling between the two ice‐sheets.
Northern hemisphere winter circulation associated with the North Atlantic Oscillation and stratospheric polar‐night jet
Authors: Kodera Kunihiko , Koide Hiroshi , Yoshimura Hiromasa
Published: September 2002

The interannual variability of the atmospheric winter circulation as characterized by the geopotential height at 500 hPa and temperature at 850 hPa, associated with the North Atlantic Oscillation (NAO) and stratospheric polar night jet (PNJ) is examined. It is suggested that the wintertime atmospheric circulation related to the NAO index can be separated into two different modes of variability. One is a regional mode, characterized by a meridional dipole type pattern in the 500 hPa geopotential height anomaly field over the Atlantic region. The other, having more zonal structure, extends over wider region of the northern hemisphere; this is also related to the lower stratospheric polar night jet. Air temperature near the surface over the eastern part of the Eurasian continent is more closely correlated with the above‐mentioned hemispheric mode of variability than the regional NAO.
Spectral fine‐structure in the polarisation of skylight
Authors: Aben I. , Helderman F. , Stam D. M. , Stammes P.
Published: September 2002

High‐spectral resolution polarisation measurements of the clear daylight sky reveal an unexpected rich spectral fine‐structure in the polarisation super‐imposed on the more familiar broad‐band continuum. This polarisation spectrum shows the spectral fingerprints of scattering and absorption processes which is illustrated with radiative transfer calculations. In particular, radiative transfer calculations suggest the potential of high‐spectral resolution polarimetry within absorption bands for remote sensing of aerosol vertical distribution, which is relevant to the Earth's radiation budget and ozone hole chemistry. In addition, the presence of spectral fine‐structure in the polarisation of skylight also has relevance to radiance measurements performed with polarisation sensitive spectrometers, such as the space‐based GOME instrument.
A map of topography on the 410‐km discontinuity from PP precursors
Authors: Flanagan Megan P. , Shearer Peter M.
Published: September 2002

We derive a new map of global topography on the 410‐km discontinuity from observations of precursors to PP obtained by stacking almost 25,000 long‐period seismograms. The inferred ‘410’ topography exhibits average peak‐to‐peak amplitude of about 30 km, has a strong degree‐one component, and is highly correlated with previous results obtained from SS precursors [Flanagan and Shearer, 1998]. Spatial variations in ‘410’ topography appear unrelated to ocean‐continent differences, suggesting that continental roots are not a significant factor in observed global temperature variations at 410 km depth.
Tidal variability of the geomagnetic polar cap mesopause above Resolute Bay
Authors: Fisher Genene M. , Killeen Timothy L. , Wu Qian , Hays Paul B. , Reeves J. M.
Published: September 2002

Variability in the geomagnetic polar cap neutral wind near the mesopause above Resolute Bay, Canada (74.9°N, 94.9°W) has been observed by a Fabry‐Perot Interferometer, using a circle‐to‐line detection technique (FPI/CLIO) to observe the OH Meinel emission. We present an analysis of the first wind measurements obtained with the FPI/CLIO from December 1995 to March 1996. The OH(7,3) (892.0 nm) Doppler winds were analyzed for tidal oscillations (defined herein as oscillations with periods which are sub‐harmonics of a solar day). Daily spectral analysis, using 50 relatively clear days showed that oscillations between, and including, 12 h and 8 h were frequent throughout the winter season in both the meridional and the zonal winds. A non‐linear least squares fit, performed on the data from the Jan 22–30 interval, revealed that a 12 h tidal feature was dominant. Observations of the OH neutral winds show variations indicating strong tidal wave activity at the mesopause.
Mobility of pyroclastic flows and surges at the Soufriere Hills Volcano, Montserrat
Authors: Calder E. S. , Cole P. D. , Dade W. B. , Druitt T. H. , Hoblitt R. P. , Huppert H. E. , Ritchie L. , Sparks R. S. J. , Young S. R.
Published: September 2002

The Soufriere Hills Volcano on Montserrat has produced avalanche‐like pyroclastic flows formed by collapse of the unstable lava dome or explosive activity. Pyroclastic flows associated with dome collapse generate overlying dilute surges which detach from and travel beyond their parent flows. The largest surges partially transform by rapid sedimentation into dense secondary pyroclastic flows that pose significant hazards to distal areas. Different kinds of pyroclastic density currents display contrasting mobilities indicated by ratios of total height of fall H, run‐out distance L, area inundated A and volume transported V. Dome‐collapse flow mobilities (characterised by either L/H or A/V2/3) resemble those of terrestrial and extraterrestrial cold‐rockfalls (Dade and Huppert, 1998). In contrast, fountain‐fed pumice flows and fine‐grained, secondary pyroclastic flows travel slower but, for comparable initial volumes and heights, can inundate greater areas.
Shear‐wave splitting across western Saudi Arabia: The pattern of upper mantle anisotropy at a Proterozoic Shield
Authors: Wolfe Cecily J. , Vernon Frank L. , Al‐Amri Abdullah
Published: September 2002

We constrain upper mantle anisotropy across the Arabian Shield from shear‐wave splitting analyses of SKS phases at eight temporary broadband stations that operated in Saudi Arabia. The direction of fast polarization is consistently aligned north‐south and the delay time between fast and slow shear waves is generally 1.0 to 1.5 s, indicating that the mantle anisotropy is relatively homogeneous and coherent. We cannot distinguish between two possible models for the origin of this signal. The observed splitting may reflect fossil upper mantle anisotropy associated with the dominantly east‐west accretion of oceanic terranes and formation of the Proterozoic Arabian lithosphere. Our results may also be compatible with present‐day asthenospheric anisotropy caused by the northward absolute plate motion of the Arabian plate or northward asthenospheric flow from an Ethiopian mantle plume.
Monitoring and modeling land subsidence at the Cerro Prieto Geothermal Field, Baja California, Mexico, using SAR interferometry
Authors: Carnec Claudie , Fabriol Hubert
Published: September 2002

Images derived from repeat‐pass spaceborne interferometric synthetic aperture radar (InSAR) systems offer the possibility of mapping surface deformation of small spatial extent and monitoring its spatio‐temporal evolution. A slow local subsidence has been detected at the Cerro Prieto geothermal field from images acquired by the European Space Agency remote sensing satellites ERS‐1/2 between 1993 and 1997. Although agricultural activity in the area limited the investigation, interferometric monitoring revealed that the ground deformation is associated with the withdrawal of geothermal fluid and agreed with the leveling data. Modeling of the subsidence was carried out assuming elastic deformation in a half‐space from simple point sources, of which five were necessary to reproduce the fringe patterns observed on the interferograms. The depths and locations of three of the sources are compatible with the location of the known reservoir. The study improves prior knowledge of the displacement field and of the mecanisms involved in the subsidence phenomenon.
Present and past climate control on fjord glaciations in Greenland: Implications for IRD‐deposition in the sea
Authors: Reeh Niels , Mayer Christoph , Miller Heinz , Thomsen Henrik Højmark , Weidick Anker
Published: September 2002

Calving of icebergs is the dominant ablation mechanism for large outlet glaciers from the Greenland ice sheet except in northernmost Greenland where bottom melting from floating glaciers dominates. This difference is controlled by present climate conditions. Glacial geological evidence indicates that the transition between the associated types of fjord‐glaciations moved north‐south in response to past climate change. In cold periods, local melt‐out of debris from the bottom of an increasing number of floating glaciers reduces the potential for iceberg transport of IRD. Thus, the marine IRD signal of Greenland origin is not a simple cold climate signal. Our findings are discussed in the context of the ongoing debate about the kind of ice transporting IRD ‐ icebergs or sea ice.
On the temporal evolution of red sprites: Runaway theory versus data
Authors: Yukhimuk V. , Roussel‐Dupré R. A. , Symbalisty E. M. D.
Published: September 2002

The results of numerical simulations of red sprite discharges, namely the temporal evolutions of optical emissions, are presented and compared with observations. The simulations are done using the recently recalculated runaway avalanche rates. The temporal evolution of these simulations is in good agreement with ground‐based photometer and CCD TV camera observations of red sprites. Our model naturally explains the ‘hairline’ of red sprites as a boundary between the region where the intensity of optical emissions associated with runaway breakdown has a maximum and the region where the intensity of optical emissions caused by conventional breakdown and ambient electron heating has a maximum. Other important characteristics of the simulated sprite such as color, shape, altitude, and intensity are in agreement with the observations as well. We also present for the first time simulations of red sprites with a daytime conductivity profile.
Fast earthward plasma flows observed in the mid/distant tail under quiet conditions: Relation to substorms
Authors: Troshichev O. A. , Kokubun S. , Kamide Y. , Mukai T. , Yamamoto T.
Published: September 2002

Measurements of the magnetic field and low energy plasma by the GEOTAIL spacecraft have been used to study fast earthward plasma flows in the distant (130–200 RE) and middle (40–80 RE) tail and their relationship to substorms. Results of the analysis show that high‐speed earthward ion flows are often observed in the mid/distant tail under conditions of low magnetic activity (AE ∼ 100 nT), when the IMF BZ component is northward or oscillates to about zero. A considerable portion of the fast earthward flows (29% in the distant tail and 53% in the middle tail) seems to be a precursor to substorm expansion onsets on the Earth. These flows occur at closed magnetic field lines. The cause and effect relationship between fast earthward plasma flows in the distant tail and substorm activity suggests that a neutral line can form at distances far beyond 100 RE during quiet conditions.
Potential high‐latitude vegetation feedbacks on CO2‐induced climate change
Authors: Levis S. , Foley J. A. , Pollard D.
Published: September 2002

We use a fully coupled climate‐vegetation model to examine the potential effects of changes in vegetation cover on simulations of CO2‐induced climate change. We find that vegetation feedbacks, acting mainly through changes in surface albedo, enhance greenhouse warming in the northern high latitudes during spring and summer months. In spring and summer, land surfaces north of 45°N are warmed by 3.3 and 1.7°C by a doubling of CO2 alone; vegetation feedbacks produce an additional warming of between 1.1–1.6 and 0.4–0.5°C, respectively. In winter, however, vegetation feedbacks appear to oppose the 5.6°C radiative warming, particularly over Eurasia. These results demonstrate that vegetation feedbacks are potentially significant and must be included in assessments of anthropogenic climate change.
Cenozoic metamorphism along the Shan Scarp (Myanmar): Evidences for ductile shear along the Sagaing Fault or the northward migration of the Eastern Himalayan Syntaxis?
Authors: Bertrand Guillaume , Rangin Claude , Maluski Henri , Han Tin Aung , Thein Myint , Myint Ohn , Maw Win , Lwin San
Published: September 2002

The Mogok metamorphic belt, exposed along the N‐S trending Shan scarp and Sagaing fault, in the eastern part of Myanmar, has been regarded as Paleozoic to Precambrian for a long time. New observations in the Shan scarp area, close to the Sagaing fault, from Thaton in the south to Mandalay in the north, allowed us to collect samples of high grade metamorphic and intrusive rocks that have been analyzed by 40Ar/39Ar step heating method. The 13 samples we analyzed provide Oligocene to Lower Miocene ages for this metamorphism. Oriented thin sections and field observations suggest that this metamorphism was caused by a NNW‐SSE to N‐S ductile extension. Therefore, we suggest that this metamorphism is not directly related to the Sagaing fault, but could be instead related to the northward migration of the eastern Himalayan syntaxis, characterized by crustal thinning, resulting from the India‐Asia oblique collision.
Can free oscillations trigger foreshocks that allow earthquake prediction?
Authors: Costello Scott W. , Tullis Terry E.
Published: September 2002

The earthquake prediction model of Whiteside and Ben‐Zion [1995] was examined to ascertain whether or not their proposed method generates statistically significant results. Their model suggests a remarkable increase in the triggering of small earthquakes by free‐earth oscillations before some large events in the vicinity of the mainshock months prior to the large event. We independently devised a program to reproduce their method and found the results to be dependent upon the number of events used in the generation of triggering percentages. Results generated using real and random data were nearly identical. We devised a parameter to remove sampling bias and test the null hypothesis, i.e., that the results using real data are no different from what is expected for random chance. The null hypothesis is upheld and there is no observed increase in this parameter in the location of the Loma Prieta earthquake prior to that event.
New observations of ultraviolet radiation and column ozone from Socorro, New Mexico
Authors: Minschwaner K.
Published: September 2002

Measurements of surface ultraviolet irradiances are presented for the period of June 1997 to December 1998 from Socorro, NM (34°N, 107°W). The observations are used with results of radiative transfer calculations to retrieve total column ozone. Mean differences between Socorro daily ozone measurements and Earth Probe TOMS satellite data are −1.8 DU and 0.6 DU for 1997 and 1998, respectively. Unusually low ozone was observed in late November and December of 1998, with levels near or below the lowest ozone in the 17‐year Nimbus‐7 and Earth Probe TOMS record for this location. The clear‐sky correlation between the UV Index at 60° solar zenith angle and total ozone is well described by a power law, with an exponent (Radiation Amplification Factor) of 0.97±0.16. One exception occurred during a 10‐day period in December 1997 and January 1998 in the aftermath of a heavy snow storm, when the UV Index exhibited clear‐sky enhancements of up to 30%. Increases in downwelling ultraviolet radiation were related to a higher effective surface albedo with maximum estimated values between 0.7 to 0.9.
Streamer disconnection events observed with the LASCO coronagraph
Authors: Wang Y. ‐M. , Sheeley N. R. , Howard R. A. , Rich N. B. , Lamy P. L.
Published: September 2002

We present Large Angle Spectrometric Coronagraph (LASCO) observations of two events that suggest magnetic disconnection in coronal streamers. During the 1–2 days preceding each event, successions of narrow looptops are seen rising slowly through the 2–6 RS field of view, forming a bright streamer stalk which continues to elongate with time. As the streamer becomes ever more constricted, it eventually severs at a heliocentric distance of ∼4 RS. The lower part of the stalk collapses back to form a cusplike structure extending to ∼3 RS, while the disconnected segment is observed as a kink or density enhancement that propagates outward with a speed of order 200 km s−1. We interpret these non‐CME events as transient openings and closings of magnetic flux rooted at the boundaries of coronal holes.
Vertical velocity statistics in continental stratocumulus as measured by a 94GHz radar
Authors: Babb D. M. , Verlinde J.
Published: September 2002

Doppler power spectra from a vertically pointing 94GHz cloud radar are used to retrieve the mean and turbulent components of the in‐cloud vertically velocities for a continental stratocumulus cloud field. Several horizontal scales of motion in the mean velocity field are shown, including a wave‐cloud feature seen in satellite photographs. A profile of vertical velocity variance is computed for both a high reflectivity and a low reflectivity regime. These profiles appear reasonable and agree well to similar statistics from an instrumented aircraft.
Vertical crustal motions from the DORIS Space‐Geodesy System
Authors: Soudarin Laurent , Crétaux Jean‐François , Cazenave Anny
Published: September 2002

Five years (1993–1997) of DORIS data on the SPOT and Topex‐Poseidon satellites have been analyzed to estimate vertical motions at 33 sites of the permanent DORIS network. Rates have been determined assuming constant velocity over the 5‐year time span. Except for a few stations, vertical rates are lower than 5 mm/yr. Comparison with solutions provided by GPS, SLR or VLBI at colocated sites shows good agreement for most stations. Some space‐geodesy vertical rates however disagree significantly. This may result from interannual to decadal fluctuations affecting the vertical motions, giving rise to different apparent linear trends if estimated over different time spans. Except for six high‐latitude stations, post‐glacial rebound produces negligible signal and cannot explain the observed motions. Other local or regional phenomena from geophysical or anthropogenic origin may be responsible for the estimated vertical motions.
Tidal influences on O2 atmospheric band dayglow: HRDI observations vs. model simulations
Authors: Marsh Daniel R. , Skinner Wilbert R. , Yudin Valery A.
Published: September 2002

Atmospheric tides perturb the temperature, winds, density, and composition of the mesosphere and lower thermosphere (MLT) and therefore affect daytime O2 atmospheric band airglow. O2 atmospheric band dayglow measurements made by the High Resolution Doppler Imager (HRDI) show clear tidal signatures in equatorial emission rates during equinox, when diurnal tide amplitudes are large. During solstice the observed symmetric diurnal variation of dayglow indicates an emission process controlled by solar absorption. Observations are compared with modeled emissions based on an atmosphere perturbed with diurnal tides predicted by the Tuned Mechanistic Tidal Model (TMTM) for March 1993. Good data/model agreement indicates enhanced emissions result from tidal advection of atomic oxygen from the lower thermosphere. While tides modulate O2 nightglow by perturbing atomic oxygen recombination rates, the tidal signatures seen in O2 dayglow are due to increased production of ozone and O(¹D). These results provide further confirmation of the consistency of the HRDI daytime wind, temperature and airglow observations.
Estimates of present‐day glacial rebound in the Lambert Glacier Region, Antarctica
Authors: Zwartz Dan , Tregoning Paul , Lambeck Kurt , Johnston Paul , Stone John
Published: September 2002

Changes in the ice load since the time of the Last Glacial Maximum (LGM) contribute to the present‐day vertical motion of the Antarctic continent. The observation of these motions will reveal information on the ice load history. Predictions of uplift rates along a transect across the Lambert Glacier region, East Antarctica, from the coast to the southernmost rock outcrops of the Prince Charles Mountains have been computed for three deglaciation scenarios. The relative vertical velocities between sites on the transect are −7 to +7 mm/yr and are large enough to be detected from continuous GPS observations taken at permanent sites over several years. When available, such information will discriminate between the currently available models for deglaciation of East Antarctica.
Models of solar irradiance variability and the instrumental temperature record
Authors: Marcus Steven L. , Ghil Michael , Ide Kayo
Published: September 2002

The effects of decade‐to‐century (Dec‐Cen) variations in total solar irradiance on global mean surface temperature Ts during the pre‐Pinatubo instrumental era (1854‐1991) are studied by using two different proxies for the irradiance and an energy‐balance climate model. Irradiance anomalies based on solar‐cycle length (CL) and solar‐cycle decay rate (CD) proxies can account for most of the warming observed up to 1976, but anthropogenic forcing is needed to explain the subsequent sharp increase in Ts. The time series of CL‐solar and anthropogenic radiative forcing resemble each other; this similarity makes it difficult to separate their effects in the instrumental Ts record. The CD‐based irradiance values reflect heuristically intensity variations in photospheric turbulence; this proxy allows one to obtain more tightly constrained values of both solar variability and terrestrial climate sensitivity from the instrumental Ts record.
Transient behavior of the meridional moisture transport across South America and its relation to atmospheric circulation patterns
Authors: Li Z. X. , Le Treut H.
Published: September 2002

The transient behavior of meridional moisture transport across the South American continent is examined with the reanalysis data provided by the European Centre for Medium‐range Weather Forecasts (ECMWF). The results show clearly the effects of the valley between the Andes and the Brazilian Plateau in canalizing the southward moisture transport: an intense jet is episodically formed in this valley. The synoptic variability of this low‐level jet and its relation to the large‐scale atmospheric circulation are studied.
Origins of the midlatitude Pacific decadal variability
Authors: Barnett Tim P. , Pierce David W. , Saravanan R. , Schneider Niklas , Dommenget Dietmar , Latif Mojib
Published: September 2002

Analysis of multiple climate simulations shows much of the midlatitude Pacific decadal variability to be composed of two simultaneously occurring elements: One is a stochastically driven, passive ocean response to the atmosphere while the other is oscillatory and represents a coupled mode of the ocean‐atmosphere system. ENSO processes are not required to explain the origins of the decadal variability. The stochastic variability is driven by random variations in wind stress and heat flux associated with internal atmospheric variability but amplified by a factor of 2 by interactions with the ocean. We also found a coupled mode of the ocean‐atmosphere system, characterized by a significant power spectral peak near 1 cycle/20 years in the region of the midlatitude North Pacific and Kuroshio Extension. Ocean dynamics appear to play a critical role in this coupled air/sea mode.
Atmospheric patterns forcing two regimes of arctic circulation: A return to anticyclonic conditions?
Authors: Johnson Mark A. , Proshutinsky Andrey Y. , Polyakov Igor V.
Published: September 2002

Atmospheric sea level pressure (SLP) patterns associated with two regimes of ice‐ocean circulation are identified by sorting the data into bins depending on whether modeled Arctic Ocean circulation was anticyclonic or cyclonic. The transition between regimes is a zonally symmetric SLP cell with maximum amplitude at the north pole. From 1946 to 1997, four anticyclonic and four cyclonic regimes track the Arctic Ocean SLP oscillation. Recent SLP data suggest that the ocean‐atmosphere system will shift, or has already shifted, to an anticyclonic state.
Simulation of rocket‐borne particle measurements in the mesosphere
Authors: Horányi Mihály , Gumbel Jörg , Witt Georg , Robertson Scott
Published: September 2002

Nanometer‐sized meteoric smoke particles and ice condensates are thought to influence the chemistry in the 80–120 km altitude region and to play an important role in the evolution of Polar Mesosphere Summer Echoes and Noctlucent Clouds. In this paper we show that aerodynamic perturbations introduced by a rocket payload complicate the analysis of dust measurements in this region. We analyze the flow of particles by applying a combined numerical simulation of flight aerodynamics and particle evolution. We show that for typical velocities of 500–1000 ms−1, the detection efficiency drops below 50% for smoke particles with radii 0.8–1.4 nm and for ice clusters with radii 2–5 nm, depending on the rocket's angle of attack. The particles are exposed to heating in the shock region, resulting in significant mass loss for ice condensates due to sublimation. Our simulations indicate that a substantial fraction of the expected nm sized meteoric smoke particles could be detected with refined instrumentation.
An investigation into shallow borehole tiltmeters
Authors: Bonaccorso Alessandro , Falzone Giuseppe , Gambino Salvatore
Published: September 2002

Shallow borehole tiltmeters are frequently used for ground deformation monitoring in volcanic areas, where they are usually installed within a few meters of the surface. A major problem concerns the noise affecting the installation at shallow depth where large tilt and strain are caused by temperature effects. The long term stability of these instruments and the best shallow depth of installation, in terms of best cost/benefit, are the crucial points. We conducted an experiment in order to compare the signals of three shallow borehole electronic tiltmeters installed in the same place at different depths. We verified the signal reliability in revealing the long term slow deformation and looked into the reduction of the temperature effects with depth. We present three years of data and discuss the limits and the advantages of the different installation depths.
High waters at Liverpool since 1768: the UK's longest sea level record
Authors: Woodworth Philip L.
Published: September 2002

An exercise of ‘data archaeology’ of high water tidal information from Liverpool, NW England has resulted in the construction of a time series of ‘Adjusted Mean High Water’ spanning 1768 to the present which can be employed as a record of proxy Mean Sea Level (MSL). The time series, although gappy, is arguably the second oldest sea level‐related record in the world, after Amsterdam's (1682, although the data we hold are from 1700 only) and of comparable age to Stockholm's (1774). It describes a secular trend for the period up to 1880 of 0.39+/−0.17 mm/year, a trend for the twentieth century of 1.22plus;/−0.25 mm/year, and an overall low frequency acceleration of 0.33+/−0.10 mm/year/century. When considered alongside geological sea level information from the area, the evidence suggests that the greater secular trend of sea level in the twentieth century, compared to long term projections derived from geological information, is primarily the result of an acceleration towards the second half of the last century, consistent with conclusions inferred from previous analyses of the very small number of other long European MSL records.
Atmosphere‐to‐snow‐to‐firn transfer studies of HCHO at Summit, Greenland
Authors: Hutterli Manuel A. , Röthlisberger Regine , Bales Roger C.
Published: September 2002

Formaldehyde (HCHO) measurements in snow, firn, atmosphere, and air in the open pore space of the firn (firn air) at Summit, Greenland, in June 1996 show that the top snow layers are a HCHO source. HCHO concentrations in fresh snow are higher than those in equilibrium with atmospheric concentrations, resulting in HCHO degassing in the days to weeks following snowfall. Maximum HCHO concentrations in firn air were 1.5–2.2 ppbv, while the mean atmospheric HCHO concentration 1 m above the surface was 0.23 ppbv. Apparent HCHO fluxes out of the snow are a plausible explanation for the discrepancy between the 0.1 ppbv atmospheric concentration predicted by photochemical modeling and the measurements. HCHO in deeper firn is near equilibrium with the lower tropospheric HCHO concentration at the annual average temperature. Thus HCHO in ice may in fact be linearly related to multi‐year average atmospheric concentrations through a temperature dependent partition coefficient.
On the photochemical production of new particles in the coastal boundary layer
Authors: O'Dowd Colin , McFiggans Gordon , Creasey David J. , Pirjola Liisa , Hoell Claudia , Smith Michael H. , Allan Beverley J. , Plane John M. C. , Heard Dwayne E. , Lee James D. , Pilling Michael J. , Kulmala Markku
Published: September 2002

Concurrent measurements of ultra‐fine (r<5 nm) particle (UFP) formation, OH and SO2 concentrations in the coastal environment are examined to further elucidate the processes leading to tidal‐related homogeneous heteromolecular nucleation. During almost daily nucleation events, UFP concentration approached ≈300,000 cm−3 under conditions of solar radiation and low tide. Simultaneous measurements of OH illustrate that, as well as occurring during low tide, these events occur during conditions of peak OH concentration, suggesting that at least one of the nucleating species is photochemically produced. Derived H2SO4 production also exhibited remarkable coherence, although phase‐lagged, with UFP formation, thus suggesting its involvement, although binary nucleation of H2SO4 and H2O can be ruled out as a plausible mechanism. Ternary nucleation involving NH3 seems most likely as a trigger mechanism, however, at least a fourth condensable species, X, is required for growth to detectable sizes. Since UFP are only observed during low tide events, it is thought that species X, or it's parent, is emitted from the shore biota ‐ without which, no nucleation is detected. Species X remains to be identified. Model simulations indicate that, in order to reproduce the observations, a nucleation rate of 107 cm−3 s−1, and a condensable vapour concentration of 5 × 107 cm−3, are required.
Simulating the response of the EOS Terra ASTER sensor to high‐temperature volcanic targets
Authors: Wright Robert , Rothery David A. , Blake Stephen , Harris Andrew J. L. , Pieri David C.
Published: September 2002

Infrared satellite data provide information regarding the thermal state and nature of activity at active volcanoes. Such radiometry has been hampered, however, by the tendency of many currently operational sensors to saturate over high‐radiance targets. Here the simulated response of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) to high‐temperature volcanic features is presented and compared to that of the Landsat Thematic Mapper (TM), which has provided the bulk of useful data since the mid 1980's. We find that ASTER's improved spectral resolution and increased dynamic range will markedly reduce the problem of sensor saturation common in TM‐based studies, thus providing valuable data previously unavailable. Saturation will still occur however, when the fractional area of high‐temperature (∼1000°C) material approaches ∼1% (∼9 m²) of ASTER's 30‐m short‐wave infrared pixels.
Plasma effects driven by electromotive force of spacecraft solar array
Authors: Sasaki Susumu
Published: September 2002

SFU(Space Flyer Unit), a 4‐ton class experimental platform, was on orbit at the height of 480 km circular for 10 months from 1995 to 1996. It carried environment diagnostic packages which contained plasma probes and wave receivers to study the plasma environment surrounding the SFU. The potential of the SFU main body during the daytime reached about 40 V negative with respect to the ambient plasma, which was driven by the electromotive force of the SFU solar array paddles(52 V). It was found that the negative potential resulted in the formation of ion flow towards the SFU main body with fluctuations in a frequency range below 100 kHz. In the sunlight, the wave receiver detected broadband fluctuations extending beyond 1 MHz. This study provides the first observation on the plasma effects of spacecraft potential biased by the solar array voltage.
Constraints placed by silicon cycling on vertical exchange in general circulation models
Authors: Gnanadesikan Anand , Toggweiler J. R.
Published: September 2002

The flux of biogenic silica out of the oceanic mixed layer (the export flux) must balance the import of high‐silicate deep waters associated with mass exchange between the surface and deep ocean. Recent regional estimates of the export flux limit it to 50–80 Tmol yr−1. In order to reproduce such low export fluxes, coarse‐resolution general circulation models must have low pycnocline diffusivity and a lateral exchange scheme which involves advection of tracers by unresolved mesoscale eddies. Failure to capture low rates of vertical exchange will result in climate models which overpredict the uptake of anthropogenic carbon dioxide and fail to capture the proper locations and rates of density transformation.
Thermal and compositional evolution of a cooling magma chamber by boundary layer Fractionation: model and its application for primary magma estimation
Authors: Kuritani Takeshi
Published: September 2002

A boundary layer fractionation model for the thermal and compositional evolution of a basaltic magma chamber is presented. The model utilizes a multicomponent thermodynamic approach for relating the compositional structure with the thermal structure of a cooling magma body. The magma composition in the main magma body evolves by transportation of a fractionated interstitial melt from the mushy boundary layer. The consideration of both the thermal and compositional evolution of the magma body enables a realistic simulation of magmatic differentiation as a function of time and space. The model is used to evaluate a primary magma estimation from volcanic rock series. It is shown that the common procedure of olivine addition gives an estimation which is significantly different from the true primary composition if the magma actually differentiated by boundary layer fractionation. This can cause significant errors in estimating the conditions at which the primary magma was generated.
Site effects as inferred from damage severity observation
Authors: Tertulliani Andrea
Published: September 2002

A long seismic sequence affecting the Umbria‐Marche region (Central Italy) started on September 26, 1997. Earthquakes with intensities up to IX MCS caused diffused damage over a large area. The resulting damage pattern is investigated, for villages settled in an intermountain basin near the epicentral area. Macroseismic data are collected and compared with the surface geology for 15 villages and hamlets within a restricted area. Among these 15 settlements, six individual groups are discernable showing a gradual variation of the damage severity. Such abrupt damage variation inside a relatively small area is influenced by modest scale lithological transitions. In particular, major effects occurred in those villages settled in the sedimentary basin close to border faults. Safest sites resulted to be those settled on bedrock and on the alluvial plane far from the edge. These observations support models existing in literature, which claim that edge effects and the generation of diffracted waves in soft basins can contribute to a stronger shaking.
Broadband measurements of the sources of explosions at Stromboli Volcano, Italy
Authors: Chouet Bernard , Saccorotti Gilberto , Dawson Phillip , Martini Marcello , Scarpa Roberto , De Luca Gaetano , Milana Giuliano , Cattaneo Marco
Published: September 2002

During September–October 1997, 21 three‐component broadband seismometers were deployed on Stromboli Volcano at radial distances of 0.3–2.2 km from the active crater to investigate the source mechanisms of Strombolian explosions. In the 2–50 s band, the very‐long period (VLP) signals associated with explosions are consistent with two stationary sources repeatedly activated in time. VLP particle motions are essentially linear and analyses of semblance and particle motions are consistent with a source centroid offset 300 m beneath and 300 m northwest of the active vents. Similar VLP waveforms are observed at all 21 stations, indicating that the seismograms are source‐dominated. The VLP ground displacement response to each explosion may be qualitatively interpreted as: (1) pressurization of the conduit associated with the ascent of a slug of gas; (2) depressurization of the conduit in response to mass withdrawal during the eruption; and (3) repressurization of the conduit associated with the replenishment of the source with fluid.
Clustering and size distributions of fault patterns: Theory and measurements
Authors: Bour Olivier , Davy Philippe
Published: September 2002

The fractal geometry of fault systems has been mainly characterized by two scaling‐laws describing either their spatial distribution (clustering) or their size distribution. However, the relationships between the exponents of both scaling‐laws has been poorly investigated. We show theoretically and numerically that the fractal dimension D and the exponent a of the frequency length distribution of fault networks, are related through the relation x=(a−1)/D, where x is the exponent of a new scaling law involving the average distance from a fault to its nearest neighbor of larger length. Measurements of the relevant exponents on the San Andreas fault pattern are in agreement with the theoretical analysis and allows us to test the fragmentation models proposed in the literature. We also found a correlation between the position of a fault and its length so that large faults have their nearest neighbor located at greater distances than small faults.
Atlantic deep circulation controlled by heating in the Southern Ocean
Authors: Hasumi Hiroyasu , Suginohara Nobuo
Published: September 2002

Thermohaline circulation has been considered to be driven by localized buoyancy loss through the sea surface at high latitudes and broadly distributed buoyancy gain elsewhere. Our numerical modeling study, however, shows that buoyancy gain for the Atlantic deep circulation is localized in the Southern Ocean. Wind‐induced upwelling there causes efficient heat transfer to the deep ocean, and controls intensity of the Atlantic deep circulation as thermohaline circulation.
GPS selective availability error contains a small component with a period of 3 seconds: Influence on the phase measurement noise
Authors: Sleewaegen J. M.
Published: September 2002

It is commonly assumed that the GPS ranging degradation called Selective Availability contains only low frequency components, with a correlation time on the order of several minutes. It will be shown here that, on top of this well known behavior, SA contains a small high frequency component centered around 1/3 Hz (period 3 s), with an amplitude on the order of the millimeter. This unexpected component will be studied and characterized. It will be shown that it causes the noise on the phase measurement to be non‐white, and that it is responsible for errors when decimating GPS data.
Atmospheric water vapor amounts retrieved from GOME satellite data
Authors: Noël Stefan , Buchwitz Michael , Bovensmann Heinrich , Hoogen Ricarda , Burrows John P.
Published: September 2002

A new method for the retrieval of global atmospheric vertical column amounts of water vapor from measurements of the Global Ozone Monitoring Experiment (GOME) is presented. The method is based on a modified Differential Optical Absorption Spectroscopy (DOAS) approach, taking into account the effects arising from strong wavelength dependent absorptions. In this paper the feasibility of this approach is demonstrated and first estimates on the retrieval precision and the accuracy of the H2O data product are given by comparison with selected Special Sensor Microwave Imager (SSM/I) data.