bluuebunny/crossref_metadata_2025 huggingface dataset:
First ice cloud effective particle size parameterization based on combined lidar and radar data
Authors: Donovan D. P. , van Lammeren A. C. A. P.
Published: October 2002

A newly developed procedure for estimating ice cloud effective particle size using combined lidar and radar signals has been applied to several months of data from the Atmospheric Radiation Measurement Program's Southern Great Plains site. Though considerable scatter is present in the retrieval results, on average, the data show a clear dependence of effective particle size on both temperature and ice water content. The data are used to construct a parameterization based on a bimodal ice particle size distribution whose characteristics depend both on temperature and ice water content.
Observation of sprites over the Asian continent and over oceans around Taiwan
Authors: Su Han‐Tzong , Hsu Rue‐Ron , Chen Alfred Bing‐Chih , Lee Yi‐Jen , Lee Lou‐Chuang
Published: October 2002

Sprites were observed over thunderstorms in the southern China and in oceans around Taiwan. The observation sites were on the Ali Mountain of Taiwan's Central Ridge area with an altitude of 2413 m and in the campus of National Cheng Kung University with an altitude of 50 m. For the observed land sprites, 90% of them were either carrots or columniforms and 64% of the sprites occurred in groups. Among the observed oceanic sprites, 89% of them were carrots but only 22% of the sprites occurred in groups. We define a sprite active system as a thunderstorm that continuously produces at least one sprite in a 10‐minute interval. The active sprites generating periods for the observed thunderstorms were typically shorter than 30 minutes. The sprite production rates for these Asian thunderstorms are estimated to be between I ≈ 2 × 10−4 events/km2/hr and I ≈ 1 × 10−3 events/km2/hr.
Spatial and temporal oxygen isotope trends at the northern tree‐line in Eurasia
Authors: Saurer Matthias , Schweingruber Fritz , Vaganov Eugene A. , Shiyatov Stepan G. , Siegwolf Rolf
Published: October 2002

The oxygen isotope ratio of ice cores and sea‐sediments is an extremely useful source of information on long‐term climatic changes. A similar approach has been applied to the oxygen isotope ratio of tree rings to enable a pattern‐based reconstruction of the isotope variations on the continents. We present an oxygen isotope map for northern Eurasia spanning from Norway to Siberia, that reflects the isotope distribution in the late 19th century, and compare it with an equivalent map for the present‐day situation. The average isotope values of 130 trees show a large east‐to‐west gradient and are highly correlated with the isotope distribution of precipitation. Surprisingly, the 18O/16O ratio of the wood has been decreasing in the interior of the continent since the late 19th century, in contrast to the strong temperature increase recorded by meteorological data. From this isotope trend over time a change in the seasonality of precipitation can be inferred.
A new coupled spectral element and modal solution method for global seismology: A first application to the scattering induced by a plume‐like anomaly
Authors: Capdeville Y. , Larmat C. , Vilotte J.‐P. , Montagner J.‐P.
Published: October 2002

The possibilities of a new numerical simulation method based on the coupling of the Spectral Element Method (SEM) with a modal solution method are illustrated by experiments focusing on the scattering induced by a localized plume‐like inclusion in a modified PREM. The plume is represented by a vertical cylindrical inclusion extending from the surface to the 660 km discontinuity. We present seismograms computed down to 50 s and assess the limits of a first order mode perturbation (Born approximation) method against the new numerical simulation.
Optical dating of Tibetan human hand‐ and footprints: An implication for the palaeoenvironment of the last glaciation of the Tibetan Plateau
Authors: Zhang David D. , Li S. H.
Published: October 2002

The Tibetan Plateau is a cold and arid environment with poor archaeological finds. It is generally assumed to have been covered by ice sheet during the last ice age. Nineteen handprints and footprints ofHomo sapienson hot spring travertine and the remnant of a fireplace have been found at an elevation of 4200 m on the Tibetan Plateau. Based on the optically stimulated luminescence of quartz extracted from samples of the baked and unheated travertine, the age of the prints and the fireplace are around 20,000. These finds suggest that there were humans living in this area around the time of the last glacial maximum (LGM), and that the ice sheet did not cover the entire Tibetan Plateau at this time.
Quasi‐decadal variation of the atmospheric CO2 seasonal cycle due to atmospheric circulation changes: 1979–1998
Authors: Higuchi K. , Murayama S. , Taguchi S.
Published: October 2002

The atmospheric CO2 seasonal cycle in the Northern Hemisphere is caused mainly by the seasonal growth and decay of the vegetation. Previous studies have attributed an increase in the seasonal cycle amplitude to an increase in the biospheric assimilation of atmospheric CO2 stimulated, particularly in high latitudes, by a warming climate and/or by land disturbances. Here we offer another plausible mechanism. Using a 3‐dimensional atmospheric transport model driven by ECMWF winds, we show that shifts in the atmospheric circulation regime can also cause inter‐annual variations and quasi‐decadal trends in the CO2 seasonal cycle amplitude that are of similar magnitude as those observed at Mauna Loa, Pt. Barrow and Alert from 1979 to 1998, independent of changes in the CO2 surface fluxes. Our results demonstrate the importance of the need to use observed winds when carrying out interpretations of observed inter‐annual atmospheric CO2 variability in terms of surface flux changes.
An estimate of strong local body forcing and gravity wave radiation based on OH airglow and meteor radar observations
Authors: Fritts David C. , Vadas Sharon L. , Yamada Yoshinori
Published: October 2002

Airglow measurements of gravity wave and smaller‐scale flow features, used together with other measurements of larger‐scale winds, provide a unique ability to quantify gravity wave dynamics at mesopause altitudes. We consider here an event observed with an OH airglow imager and the meteor radar at the MU Observatory in Japan. This was a wave breaking event of unusually large amplitude and momentum flux. Our hypothesis is that such events are relatively common, and that the resulting local forcing of the mean flow represents a vigorous source of secondary gravity waves that penetrate well into the thermosphere. Our analysis suggests a gravity wave momentum flux of ∼900 m2s−2, far larger than estimated by other techniques, and a mean flow acceleration of ∼80 ms−1 in less than an hour. We also estimate the scales and frequencies of the secondary waves resulting from this local body forcing.
Compaction control of melt distribution at fast‐spreading mid‐ocean ridges
Authors: Henstock Timothy J.
Published: October 2002

Models of mid‐ocean ridge processes in which oceanic crust forms from a sill‐like intrusion in the upper crust provide a link between geophysical studies of mid‐ocean ridges and geological studies of ophiolites. These models predict that the lower crust forms by subsidence of largely solidified material beneath the sill. Such a downwelling provides a means to counter the normal tendency of entrained melt to separate from the higher density solid phase. In this case, the melt distribution may be controlled by the melt fraction that is just unable to escape the downward motion as much as by thermal constraints. Reasonable physical parameters for such a system yield melt distributions with a good match to the observed seismic velocity structure of the East Pacific Rise. Detailed estimates of lower crustal melt distribution may help to distinguish these two controls.
Consistency of geologic and geodetic displacements during Andean orogenesis
Authors: Hindle David , Kley Jonas , Klosko Eryn , Stein Seth , Dixon Timothy , Norabuena Edmundo
Published: October 2002

Present‐day displacements within the Central Andes are being measured using high precision GPS geodesy. Until now, comparison of such ground motions within deforming plate boundary zones to those on a geologic time scale has not been possible due to lack of sufficient geological data. In the Central Andes, a comparable dataset for the past 25 Ma of mountain building can be reconstructed. Here, we use new interpretations of shortening rates averaged over 25–10 Ma and 10 Ma–present and find that whilst displacement directions have remained virtually constant and parallel, an acceleration has occurred synchronously with a slowing of convergence between the Nazca and South American plates. Geologic shortening rates in the Andes are initially ∼5–8 mm yr−1, and increase to ∼10–15 mm yr−1 whilst convergence slows from ∼150 mm yr−1 to ∼70 mm yr−1. Displacement and convergence rates inferred from GPS and marine magnetic data suggest that this trend may be continuing at present. Hence an increasing fraction of convergence is being absorbed by mountain building. This change may reflect increased plate coupling due to decreased sediment supply, younger subducting lithosphere, or increased normal stress at the interface from the effects of uplift.
InSAR observations of the 1995 Fogo, Cape Verde, eruption: Implications for the effects of collapse events upon island volcanoes
Authors: Amelung Falk , Day Simon
Published: October 2002

Fogo volcano, Cape Verde Islands, erupted in April 1995 after 43 years of dormancy. About 46 106 m3 of lava erupted during 7.5 weeks from vents on the SW flank of Pico do Fogo into Cha das Caldeiras. Interferograms obtained from 1993–1998 ERS SAR data show ground deformation due to the feeder dike but lack evidence for any volcano‐wide deformation related to volume changes of a shallow magma reservoir. This suggests that Fogo is fed from a relatively deep, mantle‐lithospheric source (>16.5 km depth), consistent with petrological data. This supports the concept that Cha das Caldeiras is the fill of a collapse scar created by a giant landslide, and not a collapse caldera overlying a central, shallow magma chamber. The disturbance of the magmatic system by giant landslides may explain why some oceanic island volcanoes with high magma supply rates currently lack well‐developed shallow reservoirs.
Tropospheric and equatorial influences on planetary‐wave amplitude in the stratosphere
Authors: Hu Yongyun , Tung Ka Kit
Published: October 2002

Using 49‐year NCEP/NCAR reanalysis data we examine two possible factors affecting the amplitudes of extratropical planetary waves in the stratosphere: tropospheric influence and equatorial Quasi‐Biennial Oscillation (QBO) modulation. Our results show that the QBO modulation on wave amplitudes is statistically significant only for wavenumber‐1 in early winter. The variability of wavenumber‐2 amplitude is mainly determined by tropospheric forcing. The effect of the solar cycle on planetary‐wave amplitude is also discussed.
A significant relation between seismic activities and reflection intensities in the Japan Trench region
Authors: Fujie Gou , Kasahara Junzo , Hino Ryota , Sato Toshinori , Shinohara Masanao , Suyehiro Kiyoshi
Published: October 2002

There is a regional variation of seismicity in the Japan trench region characterized by cluster distribution of seismically active zones which persist for at least a few decades. We conducted seismic refraction‐reflection experiments there to clarify the relationship between seismicity and crustal structure. A velocity structure model was obtained by travel‐time inversion. Although there does not seem to be distinct relationship between seismicity and the bulk velocity structure, we found a good relationship between seismicity and variation of reflective amplitude. Large amplitude reflected waves generated at the plate boundary were observed at low seismicity region and vice versa.
TOMS and METEOSAT satellite records of the variability of Saharan dust transport over the Atlantic during the last two decades (1979–1997)
Authors: Chiapello I. , Moulin C.
Published: October 2002

We combined aerosol observations of TOMS/Nimbus‐7 (1979–1993) and Meteosat/VIS (1984–1997) to investigate the variability of Saharan dust transport over the Atlantic over nearly 20 years. We first used three years (1986–1988) of coincident daily Meteosat images over the northern tropical Atlantic (15–30°N, 5–30°W) to convert the TOMS semi‐quantitative index into dust optical thickness by means of two (“winter” and “summer”) linear relationships. We then processed the whole TOMS/Nimbus‐7 archive and found that both seasonal and interannual variability of the mean dust optical thickness over the Atlantic retrieved by TOMS and Meteosat are consistent. This consistency offers an unique opportunity to monitor the export of Saharan dust over the Atlantic during the last two decades. This analysis provides the first evidence of the high year‐to‐year variability of dust transport during winter, and confirms the importance of meteorological factors, through the North Atlantic Oscillation, in affecting its occurrence at this season.
Modeling of the Eros gravity field as an ellipsoidal harmonic expansion from the NEAR Doppler tracking data
Authors: Garmier Romain , Barriot Jean‐Pierre , Konopliv Alexander S. , Yeomans Donald K.
Published: October 2002

The gravity field for asteroid 433 Eros has been determined in terms of ellipsoidal harmonic functions by processing the Doppler tracking data of the NEAR spacecraft while it was in orbit about the asteroid. Using the same set of NEAR spacecraft Doppler tracking data, comparative descriptions of the Eros gravity field are provided for both the ellipsoidal and the traditional spherical harmonic models. It is shown that for elongated bodies, like the asteroid Eros, the ellipsoidal harmonics model permits a better representation of the gravity signature than does the spherical harmonics model. Eros has a nearly uniform density but there are negative gravity anomalies near the ends of Eros and positive gravity anomalies near the Psyche crater and the Himeros depression.
Work output of planetary atmospheric engines: dissipation in clouds and rain
Authors: Lorenz R. D. , Rennó N. O.
Published: October 2002

We compute the dissipation due to the drag of falling raindrops and cloud droplets, and find both to be significant sources of dissipation on Earth and possibly Titan. On other planets, they appear to be insignificant. We compare this dissipation with the latent heat transported by the drops and the thermodynamic efficiency with which it can be converted into work. This comparison suggests moist convection on Earth and Titan is similar, but on Jupiter latent heat alone does not provide enough work to lift the condensate against gravity.
Evidence of intermediate layer characteristics in the Gadanki radar observations of the upper E region field‐aligned irregularities
Authors: Patra A. K. , Rao P. B. , Anandan V. K. , Jain A. R. , Viswanathan G.
Published: October 2002

The Gadanki VHF radar observations of the upper E region field aligned irregularities are presented. These are the first observations of low‐latitude upper E region irregularities that resemble the characteristics of intermediate layers observed over Arecibo. The most interesting aspect of these observations is their occurrence at altitudes as high as 160 km, which requires an interpretation in terms of their source mechanism. These irregularities were found to trigger about 21 LT first at higher altitude (140–160 km) and propagate downward with time. The signal intensities are found to be lower by about 12 dB and the Doppler spectra narrower by more than a factor of two compared to that of the normal E region echoes. The Doppler velocities are found to be both upward and downward with values less than 40 m s−1.
Numerical modeling of the September 13, 1999 landslide and tsunami on Fatu Hiva Island (French Polynesia)
Authors: Hébert Hélène , Piatanesi Alessio , Heinrich Philippe , Schindelé François , Okal Emile A.
Published: October 2002

On September 13, 1999, Omoa Bay (Fatu Hiva Island, French Polynesia) was struck by 2 to 5 m high water waves: several buildings were flooded and destroyed but no lives were lost. Observations gathered during a post‐event survey revealed the recent collapse into the sea of a 300 × 300 m2, at least 20‐m thick, cliff located 5 km southeast of Omoa. This cliff failure most certainly triggered the tsunami waves since the cliff was reported intact 45 min earlier. We simulate the tsunami generation due to a subaerial landslide, using a finite‐difference model assimilating the landslide to a flow of granular material. Numerical modeling shows that a 0.0024‐km3 landslide located in the presumed source area accounts for the tsunami waves reported in Omoa Bay. We show that the striking amplification observed in Omoa Bay is related to the trapping of waves due to the shallow submarine shelf surrounding the island.
On the magnitude of positive feedback between future climate change and the carbon cycle
Authors: Dufresne J.‐L. , Fairhead L. , Le Treut H. , Berthelot M. , Bopp L. , Ciais P. , Friedlingstein P. , Monfray P.
Published: October 2002

We use an ocean‐atmosphere general circulation model coupled to land and ocean carbon models to simulate the evolution of climate and atmospheric CO2 from 1860 to 2100. Our model reproduces the observed global mean temperature changes and the growth rate of atmospheric CO2 for the period 1860–2000. For the future, we simulate that the climate change due to CO2 increase will reduce the land carbon uptake, leaving a larger fraction of anthropogenic CO2 in the atmosphere. By 2100, we estimate that atmospheric CO2 will be 18% higher due to the climate change impact on the carbon cycle. Such a positive feedback has also been found by Cox et al. [2000]. However, the amplitude of our feedback is three times smaller than the one they simulated. We show that the partitioning between carbon stored in the living biomass or in the soil, and their respective sensitivity to increased CO2 and climate change largely explain this discrepancy.
Multi‐station infrasonic observations of two large bolides: signal interpretation and implications for monitoring of atmospheric explosions
Authors: Brown Peter G. , Whitaker Rodney W. , ReVelle Douglas O. , Tagliaferri Edward
Published: October 2002

Observations of two large bolides occurring over the Western Pacific on August 25, 2000 and April 23, 2001 are presented. These large bolides produced infrasonic signals at numerous stations in the Americas and Europe as well as being observed by US Department of Defence satellite sensors. The energy, location and physical characteristics of these bolides is inferred from available infrasound records and compared to satellite data. The infrasonic energy of the events from the observed signal frequencies is estimated to be 3 kT and 1 kT respectively, while the satellite energies are approximately 3 kT and 11 kT. The disagreement in energies for the April 23, 2001 (the third largest satellite observed bolide on record) event is significant and indicates acoustic/optical processes not typical of most bolides. The integrated infrasonic acoustic energy of the signals indicates that the percentage of acoustic energy deposited into the atmosphere is a minimum of ∼0.1–1% of the total source energy for each event.
An instability mechanism in the formation of the Martian lobate craters and the implications for the rheology of ejecta
Authors: Baratoux David , Delacourt Christophe , Allemand Pascal
Published: October 2002

Lobate craters are an indication of the existence of fluids in the Martian megaregolith. The emplacement of the ejecta could be similar to debris flow dynamics. In this paper we suggest that the lobate ejecta result of an instability mechanism during the surface flow. Indeed, recent experimental studies on injection of heavy viscous fluid in a lighter one show that the wavelength of the instability depends on the viscosity and density contrast between the two fluids. An extension of this 2D experiment to a cylindrical geometry has been carried out. In that case we demonstrate that a distribution of wavelengths is related to viscosity contrast. Those results have been applied to 250 single layer craters in Lunae Planum and Sinai Planum to measure the variation of viscosity with depth. The results are in agreement with a possible 1 km thick volatile rich layer above a less porous one.
Phase relations between climate proxy records: Potential effect of seasonal precipitation changes
Authors: Gildor Hezi , Ghil Michael
Published: October 2002

Phase relations between climate variables are critical in order to ascertain the main mechanisms driving glaciation cycles. Proxy records from ice cores are commonly assumed to represent annual mean averages. These averages, however, may be biased toward a particular season due, for example, to a change in the distribution of precipitation. We demonstrate using a nine‐box model of the climate system that the phase relation between atmospheric CO2 and temperature can be opposite during different seasons and, moreover, that the phase relation can change during different stages of the glacial cycle. Ice‐core records may thus favor one phase relation during certain stages over another. Our model can explain the observed lag of several thousand years of atmospheric CO2 behind temperature upon entering a stadial, given reasonable assumptions about the precipitation‐weighted temperature record at Vostok.
Investigation of glacial isostatic adjustment in the northeast U.S. using GPS measurements
Authors: Park Kwan‐Dong , Nerem R. Steven , Davis James L. , Schenewerk Mark S. , Milne Glenn A. , Mitrovica Jerry X.
Published: October 2002

We have been observing three‐dimensional site velocities at over 60 permanent GPS stations in the northeastern U.S for the purpose of inferring mantle viscosity and thus improving current models of glacial isostatic adjustment (GIA). We estimate the upper and lower mantle viscosity by comparing radial site velocities from a subset of continuous GPS measurements with numerical GIA predictions. Our inferences are consistent with previous estimates obtained using different methods and data sets.
The timing relationship between bursty bulk flows and Pi2s at the geosynchronous orbit
Authors: Yamaguchi R. , Kawano H. , Ohtani S. , Yumoto K. , Mukai T. , Saito Y. , Hayakawa H. ,   The Circum‐pan Pacific Magnetometer Network Group
Published: October 2002

The present study observationally examines relationship between Pi2 pulsations and the bursty bulk flow (BBF) in the plasma sheet. At a Pi2 onset of August 14, 1996, the GEOTAIL satellite and the GOES8 geosynchronous satellite were aligned in the X direction observing transient signatures. Those signatures were examined by referring to a ground low‐latitude Pi2 wave detected at the same meridian as GOES8. In the present event, a BBF started prior to the ground Pi2 onset, but it was preceded by a Pi2 onset at GOES8. It is also found that ground Pi2 signatures were correlated much better with geosynchronous Pi2 signatures than with perturbations of the plasma sheet flow velocity measured at GEOTAIL. These results strongly suggest that the BBF was not the cause of the low‐latitude Pi2 observed in the present event.
Does the braking of the fast plasma flow trigger a substorm?: A study of the August 14, 1996, event
Authors: Ohtani S. , Yamaguchi R. , Kawano H. , Creutzberg F. , Sigwarth J. B. , Frank L. A. , Mukai T.
Published: October 2002

In a substorm event of August 14, 1996, the Geotail satellite was at XGSM ∼ −10 RE aligned with the GOES 8 satellite in the X direction in the premidnight sector. Two Pi2 onsets were identified. Whereas the first onset was associated with a pseudobreakup, an auroral bulge developed following the second onset. At the pseudobreakup Geotail observed a fast (>900 km/s) plasma flow along with dipolarization, but the geosynchronous magnetic field became stretched subsequently. In contrast, for the main onset, the magnetic field dipolarized at GOES 8, although the associated total (time‐integrated) transport of magnetic flux at Geotail was no stronger than that for the pseudobreakup. It is suggested that the braking of the fast flow does not necessarily cause tail current disruption in a large scale, and there is an additional (or alternative) condition to suffice for an initial brightening to develop to a global substorm.
EM anomalies before the Kozani earthquake: A study of their behavior through laboratory experiments
Authors: Eftaxias K. , Kapiris P. , Dologlou E. , Kopanas J. , Bogris N. , Antonopoulos G. , Peratzakis A. , Hadjicontis V.
Published: October 2002

Strong electromagnetic (EM) anomalies have been detected, from MHz to kHz, prior to the three destructive earthquakes occurred during 1995–1999 in Greece. The observed sequence of EM anomalies before the Kozani‐Grevena earthquake (K‐G) of Ms = 6.6 on May 13, 1995 showed some important characteristics: (i) an increasing electromagnetic emission rate; (ii) an emergence of lower kHz frequencies with large amplitudes at the tail of the MHz electromagnetic anomaly; (iii) an electromagnetic quiescence approximately a few hours before the earthquake and (iv) a total absence of EM anomalies during the aftershock period. All these features are compatible with those reported by other authors. This sequence of the field observed EM signals revealed, in terms of emission pattern, similarities to the laboratory acoustic (AE) emissions during different stages of failure preparation process in rocks.
Accurate Vp:Vs relationship for dry consolidated sandstones
Authors: Arns Christoph H. , Knackstedt Mark A. , Pinczewski W. Val
Published: October 2002

We use a finite element method to study the elastic properties of dry sandstone morphologies. We show that the dry Poisson's (Vp/Vs) ratio becomes independent of the Poisson's ratio of the solid phase at a critical porosity and that this limiting behaviour holds for any number of solid phases and is insensitive to the manner in which the phases are distributed. We represent the behaviour of the Poisson's ratio as a simple flow diagram and present an empirical structure‐property relationship that holds for all Sandstone Morphologies independent of the number of phases and the Poisson's ratio of the solid phase.
“Aging” of the magnetotail thin current sheets
Authors: Zelenyi L. M. , Delcourt D. C. , Malova H. V. , Sharma A. S.
Published: October 2002

Paper is devoted to the self‐consistent analysis of thin current sheets (TCSs) formation in the presence of nonadiabatic effects. It is shown that nonadiabaticity of particle motion influences significantly the structure of “young” current sheets in which the particles have Speiser orbits. This results into the appearance of ions with large magnetic moments which reduces the current in the center of the sheet. The TCS then deteriorates, which leads to its “aging” due to the unavoidable nonadiabatic jumps of the adiabatic invariants of particle motion. When the resulting quasi‐trapped domain becomes highly populated, the current decays. The characteristic lifetime of TCS due to the chaotic nature of the system is found to be about 10–60 minutes. This effect provides a new evolutionary mechanism which finally leads to the disruption of CS structure, at least in the frames of our 1D model.
On the changing seasonality over the North Pacific
Authors: Bograd Steven , Schwing Franklin , Mendelssohn Roy , Green‐Jessen Phaedra
Published: October 2002

Although many marine organisms have life histories adapted to seasonal events in the environment, most studies aimed at understanding biotic responses to environmental variability assume a stationary and deterministic seasonal cycle, or remove it altogether. Here we use historical sea level pressure data for the period 1948–2000 to document significant changes in the amplitude and phase of the seasonal cycle in the Aleutian Low and North Pacific High, the two dominant pressure centers over the northeast Pacific Ocean. The Aleutian Low seasonal amplitude, which is dominated by the annual component, has nearly doubled over this period, mostly due to wintertime deepening. Changes in the amplitude and phase of both the annual and semi‐annual components have contributed to the time‐varying structure of the North Pacific High. Observed long‐term changes in the biological community structure and productivity of the North Pacific Ocean may be associated with this changing seasonality.
Implicit randomness in earthquakes
Authors: Wei Dongping , Chen Qi‐fu
Published: October 2002

Analytical number theory for two integers chosen at random provides a numerical method to estimate π value. An analysis of three datasets of earthquakes including earthquakes occurring in mainland China, South California, and all over the world, thus allowed us to estimate π with less than 3.0% relative deviation. The complexity of earthquakes is expressed by implicit randomness and characteristics of seismicity. If other physical precursors were not taken into account, two or more earthquakes would be correlative with one another, or an earthquake could be partly predictable on the basis of the event sequence itself, with a ratio of about 40% at most.
Spatial heterogeneity of tectonic stress and friction in the crust
Authors: Rivera Luis , Kanamori Hiroo
Published: October 2002

The complex geometry of faults, seismicity, and diversity of earthquake mechanisms suggest that the stress and strength in Earth's crust are spatially heterogeneous. We investigated the degree of heterogeneity using the following two end‐member models. In one end‐member model, we assumed that the orientation of stress is uniform in the crust as is assumed in many stress inversion studies. In this model, the variability of earthquake mechanisms means that friction during faulting must vary for each event. We computed friction μ from the ratio of the resolved shear stress to the effective normal stress on the fault plane with the assumption of hydrostatic pore pressure. The values of μ vary over a large range from 0 to 1.5. In the other extreme model we assumed optimally oriented slip and a constant μ = 0.6, as is suggested by Byerlee's law, for all the earthquakes, and determined the local stress orientation for each earthquake. The orientation of the stress changes drastically from one earthquake to another, and the assumption of uniform stress field commonly used in stress inversion is not warranted. An important conclusion is that a regionally uniform stress field and constant friction on optimally oriented faults are mutually exclusive. The actual situation in the crust is most likely to be intermediate between these two end‐member models. From the existing data alone, we cannot determine the degree of heterogeneity uniquely, but both μ and the local stress field near earthquake faults are likely to vary substantially, and studies on earthquake rupture dynamics must take these heterogeneities into consideration.
Decadal variability of the North Pacific Polar Front: Subsurface warming versus surface cooling
Authors: Belkin Igor , Krishfield Richard , Honjo Susumu
Published: October 2002

Over 200 hydrographic sections are used to trace the Polar Front defined as the southern boundary of the “pure” subarctic stratification with a pronounced, extremely cold, subsurface temperature minimum underlain by a temperature maximum. The front extends from 40°N off Japan to 57°N in the Gulf of Alaska where it retroflects and continues WSW with the Alaskan Stream. The front's decadal variability from 1977–1999 is examined along 150°E, 170°E, 175.5°E, and 180°E. At these longitudes the front is relatively stable, except for 170°E, where it shifts north‐south by 400 km every 6 years. Most time series reveal a subsurface warming of ∼1°C per decade, and a surface cooling, of the front. Since the subsurface temperature minimum is a remnant of winter convection, the subsurface warming signals an amelioration of the winter climate, whereas the summer climate becomes colder.
Simulated changes of the Indian summer monsoon under enhanced greenhouse gas conditions in a global time‐slice experiment
Authors: May Wilhelm
Published: October 2002

In this study the possible change of the Indian summer monsoon associated with the anticipated increase in the greenhouse gases concentrations is investigated. This is done on the basis of a time‐slice experiment performed with the ECHAM4 atmospheric GCM at a high horizontal resolution of T106. The first time‐slice (1970–1999) represents the present‐day climate and the second one (2060–2089) the future climate. The time‐slice experiment predicts an intensification of the rainfall in the Indian region during the monsoon season due to the general warming, while the future changes in the large‐scale flow indicate a weakening of the monsoon circulation. The increase of the regional rainfall is related to an intensification of the atmospheric moisture transport into the Indian region.
Sulfuric acid measurements in the exhaust plume of a jet aircraft in flight: Implications for the sulfuric acid formation efficiency
Authors: Curtius J. , Arnold F. , Schulte P.
Published: October 2002

Sulfuric acid concentrations were measured in the exhaust plume of a B737‐300 aircraft in flight. The measurements were made onboard of the German research aircraft Falcon using the Volatile Aerosol Component Analyzer (VACA). The VACA measures total H2SO4, which is the sum of gaseous H2SO4 and aerosol H2SO4. Measurements took place at distances of 25–200 m behind the B737 corresponding to plume ages of about 0.1–1 seconds. The fuel sulfur content (FSC) of the fuel burned by the B737 engines was alternatively 2.6 and 56 mg sulfur per kilogram fuel (ppmm). H2SO4 concentrations measured in the plume for the 56 ppmm sulfur case were up to ∼600 pptv. The average concentration of H2SO4 measured in the ambient atmosphere outside the aircraft plume was 88 pptv, the maximum ambient atmospheric H2SO4 was ∼300 pptv. Average efficiencies εΔCO2 = 3.3 ± 1.8% and εΔT = 2.9 ± 1.6% for fuel sulfur conversion to sulfuric acid were inferred when relating the H2SO4 data to measurements of the plume tracers ΔCO2 and ΔT.
Geometry of Proterozoic sutures in the central Rocky Mountains from seismic reflection data: Cheyenne belt and Farwell Mountain structures
Authors: Morozova Elena , Wan Xin , Chamberlain Kevin R. , Smithson Scott B. , Morozov Igor B. , Boyd Nickolas K. , Johnson Roy A. , Karlstrom Karl E. , Tyson Amanda R. , Foster C. T.
Published: October 2002

Seismic reflection data show ∼40° S‐dipping reflectors that extend from the Cheyenne belt (CB‐Archean‐Proterozoic suture) to 20 km depths, and profound differences in crustal reflectivity across the suture zone, which is itself imaged as an interwedging boundary. Archean crust has a Moho reflection (at 40 km) and abundant upper crustal reflectivity; Proterozoic crust has no Moho reflection and is distinctly less reflective. Reflective zones south of the Cheyenne belt include 40° S‐ and N‐dipping reflections that extend from the Farwell Mountain zone to 20 km depths; these are interpreted to be a complex cryptic suture zone between the 1.78–1.76 Ga Green Mountain block and 1.75–1.72 Ga Rawah block.
Relation between Pressure Balance Structures and polar plumes from Ulysses high latitude observations
Authors: Yamauchi Yohei , Suess Steven T. , Sakurai Takashi
Published: October 2002

Ulysses observations have shown that pressure balance structures (PBSs) are a common feature in high‐latitude, fast solar wind near solar minimum. Previous studies of Ulysses/SWOOPS plasma data suggest these PBSs may be remnants of coronal polar plumes. Here we find support for this suggestion in an analysis of PBS magnetic structure. We used Ulysses magnetometer data and applied a minimum variance analysis to magnetic discontinuities in PBSs. We found that PBSs preferentially contain tangential discontinuities, as opposed to rotational discontinuities and to non‐PBS regions in the solar wind. This suggests that PBSs contain structures like current sheets or plasmoids that may be associated with network activity at the base of plumes.
Inner Core Transition Zone and Anomalous PKP(DF) Waveforms from Polar Paths
Authors: Song Xiaodong , Xu Xiaoxia
Published: October 2002

Short‐period PKP(DF) waves (which travel through the inner core) from polar paths (nearly NS) were observed to have small amplitudes and complex waveforms but the cause has been a mystery. Here we examine both short‐period and broadband PKP record sections from a single earthquake in South Sandwich Islands (SSI). The data from polar paths show clear evidence for an inner core triplication. Our waveform modeling suggests a 250‐km thick isotropic upper inner core (UIC) overlying an anisotropic lower inner core (LIC) with about 8% anisotropy. The synthetics match the observed waveforms and amplitudes well with a normal value of inner core attenuation. We propose that such a UIC/LIC transition zone structure may be the cause of anomalous DF waveforms along polar paths. The inferred level of anisotropy in the LIC, 2–3 times previous estimates, has important implications for understanding physical properties of the inner core and sources of inner core anisotropy.
A coupled atmospheric‐hydrological modeling study of the 1996 Ha! Ha! River basin flash flood in Québec, Canada
Authors: Lin Charles A. , Wen Lei , Béland Michel , Chaumont Diane
Published: October 2002

We use a high‐resolution regional atmospheric model coupled to a hydrological model, and an off‐line routing module to simulate a hydrograph during the 1996 July flash flood that occurred in the Saguenay region of eastern Québec. The hydrograph is at the outlet of the Ha! Ha! Lake in the Ha! Ha! River basin. The former has a drainage area of 250 km2 and is covered by 6 model grid squares; the precipitation at these grid squares compare well with observations at the nearest available rain gauge located 20 km south of the basin. The hydrological model is a modified version of a land surface scheme which consists of three soil layers, and the routing module is based on the geomorphological unit hydrograph. The simulated hydrograph is compared with another reconstructed hydrograph in the published literature.
Centrifugal acceleration of ions near Mercury
Authors: Delcourt D. C. , Moore T. E. , Orsini S. , Millilo A. , Sauvaud J.‐A.
Published: October 2002

We investigate the parallel acceleration of ions inside Mercury's magnetosphere. We focus on centrifugal effects associated with the large scale plasma convection. We demonstrate that, because curvature radii of the E × B drift paths are much smaller at Mercury than at Earth, centrifugal effects are enhanced and lead to prominent parallel energization during transport from high to low latitudes. For moderate convection rates, model trajectory calculations reveal that these E × B related centrifugal effects yield energization of heavy ions sputtered from Mercury's surface (e.g., Na+) of several tens or a few hundreds of eV within minutes. This suggests that, at Mercury, material of planetary origin is rapidly raised up to plasma sheet energies. Such a situation contrasts with that prevailing at Earth where these centrifugal effects are relatively weak, yielding energization of ionosphere originating ions of at most a few tens of eV on the time scale of hours.
Effects of crust and mantle heterogeneity on PP/P and SS/S amplitude ratios
Authors: Ritsema Jeroen , Rivera Luis A. , Komatitsch Dimitri , Tromp Jeroen , van Heijst Hendrik‐Jan
Published: October 2002

Long‐period (T > 16 s) PP/P and SS/S amplitude ratios have coherent geographic variations. On average, PP/P is ∼10% higher than predicted by the Preliminary Reference Earth Model (PREM) when PP surface‐reflection points are within continental regions, and ∼10% lower than PREM predictions for oceanic reflection points. Spectral‐element synthetics show that this variation can be attributed mostly to the effect of crustal thickness on the long‐period PP reflection coefficient. The anomalies of SS/S are similar in amplitude but their geographic variation does not obviously correlate with ocean/continent variations. The variation of SS/S determined from spectral‐element waveforms of S and SS for 3‐D models of the crust and mantle is similar to the observed variation of SS/S. This suggests that wave propagation effects are largely responsible for the observed SS/S variation, not only intrinsic attenuation.
Mantle discontinuities beneath Southern Africa
Authors: Gao Stephen S. , Silver Paul G. , Liu Kelly H. ,   Kaapvaal Seismic Group
Published: October 2002

Seismic velocity discontinuities within the top 1000 km of the Earth beneath southern Africa are imaged by stacking about 1300 source‐normalized broadband seismograms recorded by the Southern African Seismic Experiment. The Moho, 410, and 660 kilometer discontinuities are clearly detected. The mean mantle transition zone thickness is 245 km, essentially the same as the global average, suggesting that the transition zone is not anomalously warm. Thus, the lower‐mantle ‘African Superplume’ beneath our study area has no discernible effect on transition zone temperature and is consequently confined to the lower mantle. Variations in transition zone thickness appear to be related to the presence or absence of thick lithosphere. We do not detect several previously‐reported discontinuities beneath continents, such as the Hales or Lehmann discontinuities, and find no evidence for a 520 km discontinuity, nor do we detect a previously proposed low‐velocity zone just above the transition zone.
Seismic Quiescence before the 2000 M = 7.3 Tottori earthquake
Authors: Huang Qinghua , Nagao Toshiyasu
Published: October 2002

We investigated the characteristics of the seismic quiescence associated with the 2000 M = 7.3 Tottori earthquake by applying the Region‐Time‐Length (RTL) algorithm to the earthquake catalog of the Japan Meteorological Agency (JMA). We calculated the RTL parameters at the epicenter after eliminating aftershocks from the catalog and estimating its completeness. The RTL parameters at the epicenter indicated that a seismic quiescencce started in 1999 and reached its minimum in May, 2000. This quiescence is unlikely an artifact due to the changes of model parameters. The close investigation indicated that the quiescence, which appeared in a broad region around the epicenter during 1999–2000, is the only alarm group in study space and time and is therefore most probably a precursor of the Tottori earthquake. The seismicity changes revealed in this study may give better understanding of the seismo‐tectonics in the region and the preparation process of the Tottori earthquake.
Teleconnection of OLR and SST anomalies over Atlantic Ocean with Indian summer monsoon
Authors: Srivastava A. K. , Rajeevan M. , Kulkarni R.
Published: October 2002

The present study discusses the teleconnection between outgoing longwave radiation (OLR) and sea surface temperature (SST) anomalies over North Atlantic Ocean and the Indian Summer Monsoon Rainfall (ISMR). It has been found that OLR and SST anomalies over North Atlantic Ocean during the month of May, which are the manifestations of the North Atlantic Oscillation (NAO), show statistically significant correlations with ISMR. The index of area averaged OLR anomaly over North Atlantic Ocean has a correlation of −0.82 with ISMR for the period 1979–2000. These relationships are found to be stronger and stable during the recent years. Possible physical mechanisms of this teleconnection have also been discussed.
Driven Alfven waves and electron acceleration: A FAST case study
Authors: Chaston C. C. , Bonnell J. W. , Peticolas L. M. , Carlson C. W. , McFadden J. P. , Ergun R. E.
Published: October 2002

Observations of electric and magnetic field oscillations and accelerated electron distributions within an inverted‐V region suggest the propagation of an Alfven wave from the outer magnetosphere into the auroral acceleration region. This hypothesis is tested for a case study event by simulating the propagation of an Alfven wave driven by an oscillating potential in the outer magnetosphere. At the spacecraft altitude the waveform and the associated electron distributions and spectra formed due to acceleration in the Alfven wave field are similar to those observed. The results show that more than 50% of the downgoing wave Poynting flux is dissipated through electron acceleration parallel to the geomagnetic field.
Europa: Tidal heating of upwelling thermal plumes and the origin of lenticulae and chaos melting
Authors: Sotin Christophe , Head James W. , Tobie Gabriel
Published: October 2002

Tidal heating models are linked to thermal convection models for ice having strongly temperature dependent viscosity. In the range of ice viscosity inferred from laboratory experiments, tidal forces will heat up rising diapirs on Europa. Partial melt produced in the rising diapirs is predicted to create disruption of near‐surface materials and formation of lenticulae and chaos, even if the average ice layer thickness overlying an ocean is larger than 20 km.
First in‐situ observation of night‐time F region currents with the CHAMP satellite
Authors: Lühr H. , Maus S. , Rother M. , Cooke D.
Published: October 2002

The CHAMP satellite in its polar, low‐Earth orbit (450 km altitude) is a suitable platform for studying F region currents. High precision magnetic field measurements are used to detect and characterize these upper ionospheric currents on the Earth's nightside. A few examples are presented to illustrate the special features of the currents and a statistical study is performed on half a year of data revealing their global distribution. We find a spatial confinement of the currents to the near‐equatorial region bounded by the Appleton anomaly and their appearance in the pre‐midnight sector. The distribution with longitude exhibits high occurrence rates in the Atlantic sector and very few events in the Indian sector. The currents flow generally westward at a height‐integrated current density of several mA/m. Small‐scale fluctuations observed in current intensity are interpreted as an indication for plasma instabilities in the F region. Our analysis indicates that the appearance of F region currents is coupled with the presence of plasma bubbles.
Precipitation of auroral protons in detached arcs
Authors: Immel Thomas J. , Mende Stephen B. , Frey Harald U. , Peticolas Laura M. , Carlson Charles W. , Gérard Jean‐Claude , Hubert Benoit , Fuselier Stephen A. , Burch James. L.
Published: October 2002

Recent global‐scale observations by the IMAGE‐FUV instrument demonstrate the existence of regions of particle precipitation at sub‐auroral latitudes on the dayside. The signature of this precipitation is seen infrequently, but when so, it is clear in all 3 channels of the FUV instrument. A conjugate hemisphere conjunction with the FAST satellite demonstrates the presence of precipitating protons and the notable absence of precipitating electrons in these arcs. With this knowledge, one can determine the mean energy and energy flux of the precipitating protons by intercomparison of the response in the three FUV channels. Assuming that the protons have a kappa energy distribution, the mean energy is found to be ∼20 keV, with a peak in total energy flux of ∼1 mW/m2/sec, consistent with fits to the FAST ion measurements. These phenomena are observed mainly during times of high solar wind dynamic pressure and variable interplanetary magnetic field, and are associated with earlier nightside enhancements in the brightness and latitudinal extent of the proton aurora.