bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion microprobe U‐Pb dating and REE analyses of phosphates in H4‐chondrite, Yamato‐74371
Authors: Terada Kentaro , Sano Yuji
Published: October 2002

U and Pb isotopes and rare earth elements (REEs) in individual phosphate grains from H4‐chondrites, Y‐74371 were measured by using an ion microprobe. Nine analyses of whitlockite (merrillite) and five analyses of apatites indicate a total Pb/U isochron age of 4533 ± 40 Ma (2 sigma), which are consistent with the results from previous using Thermal ionization mass spectrometer (TIMS). The observed apatites age of 4525 ± 30 Ma (2 sigma), however, is younger than those of previous works. On the other hand, the time difference between the whitlockite age of 4601 ± 94 Ma (2 sigma) and those of apatites are not observed, because of the large uncertainties. The REE abundance patterns of the whitlockites normalized to CI chondrite are characterized by an almost constant enrichment of 200–800 times CI abundance, and a striking negative Eu anomaly. The REE abundances of the apatites are lower than those of whitlockite grains, and vary appreciably among different grains. The remarkable correlation between the Eu anomaly (Eu/Eu*) and total concentration of REE is confirmed, but significant correlation with Eu anomaly and formation age of individual grains are not observed.
An examination of anomalously low column ozone in the Southern Hemisphere midlatitudes during 1997
Authors: Cordero Eugene C. , Nathan Terrence R.
Published: October 2002

Observations from both ground‐based and satellite instruments show record low column ozone abundance between 20°S and 40°S during 1997. The 1997 monthly averaged column ozone from the Total Ozone Mapping Spectrometer (TOMS) is up to 25 Dobson units (DU) lower than the TOMS climatological mean (1979–1996) and up to 20 DU below the previous record low values. Observations from the Halogen Occultation Experiment show that below average ozone concentrations during 1997 were confined primarily to the lower stratosphere. Residual circulation statistics calculated from the United Kingdom Meteorological Office temperature analyses indicate that circulation anomalies during 1997 can account for ∼5–10 DU/month decrease in column ozone between 20°S and 50°S. At these latitudes during 1997, structural characteristics of the ozone and residual circulation fields both suggest a connection with the equatorial quasi‐biennial oscillation.
The sudden increase of solar and geomagnetic activity after 1923 as a manifestation of a non‐linear solar dynamo
Authors: Duhau S. , Chen Ch. Y.
Published: October 2002

There are some indications that the coupling function between the polar and the toroidal solar magnetic field strengths are time dependent. Therefore, as proxy data of these strengths, the relationship between long‐term modulation of solar and geomagnetic activity is analyzed here by means of a wavelet multi‐resolution analysis of yearly means of sunspot number and geomagnetic index aa since 1844. It is found that aa index and relative sunspot number long‐term modulations oscillate around constant levels that have increased to be 1.9 and 1.6, respectively of its values prior 1923. The oscillations of the aa and Rz long‐term modulation appear to be well represented by the superposition of a decadal cycle and the Gleissberg cycle. The amplitude ratio and the phase shift between the Rz and aa decadal cycles changed sharply at year 1923, and the Gleissberg cycle was interrupted to be restarted at year 1949. The synchronicity of these changes with temporal changes in several solar and solar‐terrestrial variables indicates that the non‐linear nature of the solar dynamo has lead to a major change of its background state after 1923.
Global ocean warming tied to anthropogenic forcing
Authors: Reichert Bernhard K. , Schnur Reiner , Bengtsson Lennart
Published: October 2002

Observed global ocean heat content anomalies over the past five decades agree well with an anthropogenically forced simulation using the European Center/Hamburg coupled general circulation model (GCM) ECHAM4/OPYC3 considering increasing greenhouse gas concentrations, the direct and indirect effect of sulphate aerosols, and anthropogenic changes in tropospheric ozone. An optimal detection and attribution analysis confirms that the simulated climate change signal can be detected in the observations in both the upper 300 m and 3000 m of the water column and that the observed changes in ocean heat content are consistent with those expected from the anthropogenically forced GCM integration. This suggests that anthropogenic forcing is a likely explanation for the observed global ocean warming over the past five decades.
Isotopic fractionation of carbonyl sulfide in the atmosphere: Implications for the source of background stratospheric sulfate aerosol
Authors: Leung Fok‐Yan T. , Colussi Agustín J. , Hoffmann Michael R. , Toon Geoffrey C.
Published: October 2002

In order to assess the contribution of carbonyl sulfide to stratospheric sulfate aerosol (SSA), we examined the stratospheric OC34S and OC32S concentration profiles in the infrared limb‐transmittance spectra acquired by the JPL MkIV instrument. We found that OC34S is preferentially depleted by solar photolysis. The derived 34S enrichment factor: ε = +73.8 ± 8.6‰, in conjunction with literature values of δ34S ∼ +11‰ for tropospheric OCS, and a ∼ 10% net processing of the OCS transported upwardly into the stratosphere, suggests that aerosol sulfate proceeding from OCS should be highly enriched in δ34S ∼ 80‰, comparing our prediction with previous reports of δ34S ∼ +2.6‰ for background SSA, we infer either that OCS is a minor contributor to SSA or that current views about its 34S‐abundance and atmospheric circulation are seriously flawed.
Ionospheric and dayglow responses to the radiative phase of the Bastille Day flare
Authors: Meier R. R. , Warren H. P. , Nicholas A. C. , Bishop J. , Huba J. D. , Drob D. P. , Lean J. L. , Picone J. M. , Mariska J. T. , Joyce G. , Judge D. L. , Thonnard S. E. , Dymond K. F. , Budzien S. A.
Published: October 2002

The Sun's Bastille Day flare on July 14, 2000 produced a variety of geoeffective events. This solar eruption consisted of an X‐class flare followed by a coronal mass ejection that produced a major geomagnetic storm. We have undertaken a study of this event beginning with an analysis of the effects of the radiative phase of the flare on the dayglow and the ionosphere. The key new enabling work is a novel method of evaluating the X‐ray and extreme ultraviolet (EUV) solar spectral irradiance changes associated with the flare. We find that the solar radiative output enhancements modeled during the flare are consistent with measurements of both solar EUV irradiance and far UV Earth thermospheric dayglow. We use the SAMI2 model to predict global ionospheric changes along a magnetic meridian that show significantly different northern and southern effects, suggesting that flares can be used to study ionospheric dynamics.
On the solar cycle dependence of the N+/O+ content in the magnetosphere and its relation to atomic N and O in the Earth's exosphere
Authors: Mall U. , Christon S. , Kirsch E. , Gloeckler G.
Published: October 2002

We investigate a solar cycle dependence of singly charged Nitrogen and Oxygen over a five‐year period from 1995–2000 on the nightside of the Earth's magnetosphere using instrumentation on the WIND spacecraft. We show that N+, another heavy ion that is of terrestrial origin, is a large fraction of O+, and it contributes significantly to magnetospheric plasma. We find that the N+/O+ ratio has a solar cycle relationship with a higher value of this ratio at solar minimum than at solar maximum. We examine the N+/O+ ratio against thermospheric N/O MSIS 86 model calculations which exhibit no solar cycle variation.
Field‐aligned ionospheric current systems observed from Magsat and Oersted satellites during northward IMF
Authors: Stauning P.
Published: October 2002

Combination of Magsat and Oersted high‐precision magnetic measurements has provided detailed and consistent patterns of ionospheric field‐aligned current (FAC) patterns during intervals of northward interplanetary magnetic field (NBZ) conditions. Our analysis has revealed that the NBZ FAC currents extend from two rounded or bean‐shaped ionospheric regions centered at 85° geomagnetic latitude and magnetic local times of approximately 0900 for the upward and 1500 for the downward FAC. The locations of the NBZ FAC regions are almost invariant to seasonal variations and to variations in the magnitude of IMF Bz. The NBZ FAC currents are sizeable for summer conditions only and vanishes during equinox and winter seasons. The NBZ FAC intensity is a strongly non‐linear function of IMF Bz with a marked threshold at around +5 nT. The observed characteristics indicate that the NBZ currents are the competing high‐latitude counterpart of the region 1 (R1) low‐latitude boundary layer currents.
Influence of confining pressure on the mechanical and structural evolution of laboratory deformation bands
Authors: Mair Karen , Elphick Stephen , Main Ian
Published: October 2002

We present experimental observations of the influence of confining pressure on the mechanical behavior and structural style of damage in porous quartz rich sandstones. Large (100‐mm diameter) samples of sandstone are deformed in a triaxial deformation apparatus, resulting in deformation expressed as pale interweaving bands of granulated material with finite shear offset and associated microcracking. The deformation fabrics evolve systematically from localized to more pervasive geometries with increasing confining pressure, associated with a systematic reduction in dynamic stress drop. The initial failure envelope is consistent with Mohr‐Coulomb frictional behavior for all tests. These mechanical and structural observations confirm a gradual transition between brittle and semi‐brittle behavior below the threshold for bulk cataclastic flow in a porous granular medium. Our experiments demonstrate that deformation band formation is strongly pressure‐sensitive. The resulting structures are likely to have a strong anisotropic influence on permeability.
Ozone feedback stabilizes the quasi‐biennial oscillation against volcanic perturbations
Authors: Tanii Ryuta , Hasebe Fumio
Published: October 2002

Possible interference by volcanic aerosols with downward propagating quasi‐biennial oscillation (QBO) in the equatorial stratosphere has been studied by using a mechanistic model that incorporates the feedback of ozone through short wave absorption. The ascending motion driven by the radiative heating due to volcanic aerosols could be combined with the QBO‐induced upward motion to block the descent of the easterly shear zone of the QBO when the ozone feedback is not taken into account. However, as the ozone concentration in the cold easterly shear zone is relatively low and the aerosol‐driven vertical ozone advection makes its concentration still lower, the negative anomalies of solar heating due to perturbed ozone compensate for the aerosol‐induced diabatic heating. Thus the interactions between dynamics and radiation intermediated by the ozone feedback play an important role in stabilizing the time evolution of the QBO against perturbations by volcanic aerosols.
Continuous monitoring of propagation velocity of seismic wave using ACROSS
Authors: Ikuta Ryoya , Yamaoka Koshun , Miyakawa Koji , Kunitomo Takahiro , Kumazawa Mineo
Published: October 2002

Temporal variations in the P‐ and S‐wave travel times were continuously monitored using ACROSS, which is a newly developed system for utilizing accurately controlled continuous sinusoids for seismic exploration. We made an experiment lasting for 15 months at a site near the Nojima fault which ruptured during the 1995 Kobe earthquake (M7.2). The elastic waves emitted from the ACROSS vibrators located at the surface were observed with seismometers at 800 m and 1700 m depth. The long‐term variations of about 2 ms for both the P and S waves were observed during the 15‐month experiment. The major cause of these variations is identified to be that of a near‐surface property which changes the near‐source vibration. The variations in the deeper structures estimated after the reduction of the near‐source variation were about 0.5 ms. An S‐wave delay of about 1 ms was detected due to the 2000 Western Tottori earthquake (M6.6).
Effective elastic thickness and heat flux estimates on Ganymede
Authors: Nimmo Francis , Pappalardo Robert T. , Giese Bernd
Published: October 2002

We identify sites of apparent flexural uplift at rift zone boundaries on Ganymede using Galileo stereo‐derived topography. The estimated effective elastic thickness te is 0.9–1.7 km for a nominal Young's modulus of 1 GPa. Using a viscoelastic model of the ice crust we find that the temperature defining the base of the elastic layer is <185 K for likely strain rates. The inferred local heat flux during deformation is less than 245 mW m−2, and probably close to 100 mW m−2. The stresses required to cause fault motion are around 1 MPa. Both the high heat flux and the high stresses are consistent with estimates of these quantities during an episode of transient tidal heating in Ganymede's past.
Remote ion temperature measurements of Earth's magnetosphere: Medium energy neutral atom (MENA) images
Authors: Scime E. E. , Keesee A. M. , Jahn J.‐M. , Kline J. L. , Pollock C. J. , Thomsen M.
Published: October 2002

Energy spectra of ENA images obtained with the MENA imager on the IMAGE observatory are used to construct remote images of the plasma ion temperature. The remotely measured ion temperatures are consistent with in‐situ ion temperature measurements. During the storm of August 12, 2000, the ion temperatures on the dawn side of the magnetosphere are significantly lower than the dusk side ion temperatures. Similar observations of ion temperature asymmetry are presented for three other storm periods.
80 yr oscillation of summer rainfall over North China and East Asian Summer Monsoon
Authors: Zhu Jinhong , Wang Shaowu
Published: October 2002

Relationship between summer rainfall over the eastern part of China (east of 110°E) and East Asian Summer Monsoon (EASM) is studied based on summer rainfall coded levels data set for the period of 1470–1999, rain gauge data set for the period of 1951–1999 and sea level pressure (SLP) for the period of 1873–1997. The distinct 80 yr oscillation of summer rainfall is found over North China (near 35°–40°N and east of 110°E), southern part of Northeast China (south of 42°N in Northeast China), lower‐middle Yangtse River valley (east of 110°E along Yangtse River) and South China (south of 25°N and east of 110°E). This oscillation over North China is in phase with that over South China and out of phase to that along lower‐middle Yangtse River valley. Summer rainfall over North China correlates negatively with averaged SLP for the area near (105°–115°E and 30°–35°N), but positively with averaged SLP for the area near (120°–130°E and 20°–25°N). Therefore, an index of EASM is defined using the difference of averaged SLP over the above two regions. Summer rainfall over North China is greater than normal and drought occurs along lower‐middle Yangtse River valley when strong EASM reaches North China. On the contrary, drought is found over North China and flood appears along lower‐middle Yangtse River valley when EASM is close to normal or weak. Finally, the interdecadal variability of EASM is studied using long‐term summer rainfall coded levels data set over North China during the past 530 yr.
On the slip‐weakening behavior of rate‐ and state dependent constitutive laws
Authors: Cocco Massimo , Bizzarri Andrea
Published: October 2002

We study the dynamic traction behavior within the cohesive zone during the propagation of earthquake ruptures adopting rate‐ and state‐dependent constitutive relations. The resulting slip‐weakening curve displays an equivalent slip‐weakening distance (D0eq), which is different from the parameter L controlling the state variable evolution. The adopted constitutive parameters (a, b, L) control the slip‐weakening behavior and the absorbed fracture energy. The dimension of the nucleation patch scales with L and not with D0eq. We propose a scaling relation between these two lengthscale parameters which prescribes that D0eq/L ∼ 15.
The impact of the South‐American plate motion and the Nazca Ridge subduction on the flat subduction below South Peru
Authors: van Hunen Jeroen , van den Berg Arie P. , Vlaar Nico J.
Published: October 2002

Flat subduction near Peru occurs only where the thickened crust of the Nazca Ridge subducts. Furthermore, the South‐America continent shows a westward absolute plate motion. Both the overriding motion of South‐America and the subduction of the Nazca Ridge have been proposed to explain the flat slab segment below South Peru. We have conducted a series of numerical model experiments to investigate the relative importance of both mechanisms. Results suggest that the average upper mantle viscosity should be about 3.5 × 1020 Pa s or less and basaltic crust should be able to survive 600 to 800°C ambient temperature before transforming into eclogite to explain the slab geometry below Peru. The effect of the overriding plate is estimated to be as large or twice as large as that of the plateau subduction.
Noble gases and radiocarbon in natural gas hydrates
Authors: Winckler Gisela , Aeschbach‐Hertig Werner , Holocher Johannes , Kipfer Rolf , Levin Ingeborg , Poss Christian , Rehder Gregor , Suess Erwin , Schlosser Peter
Published: October 2002

In samples of pure natural gas hydrates from Hydrate Ridge, Cascadia Margin, virtually no helium and neon components are present providing evidence that the light noble gases are not incorporated into the structure of natural methane hydrates. In contrast, the hydrates contain significant amounts of argon, krypton and xenon. These gases show a distinct fractionation pattern, with the heavier ones preferentially incorporated into the gas hydrate structure. The hydrate methane is devoid of 14C indicating that there is no contribution of a recent (14C‐active) organic carbon reservoir to the hydrate carbon pool. On the basis of the δ13C and δ2H signature, it appears that microbial CO2‐reduction is the dominant CH4 production pathway.
Ice mass loss in Antarctica and stiff lower mantle viscosity inferred from the long wavelength time dependent gravity field
Authors: Sabadini R. , Di Donato G. , Vermeersen L. L. A. , Devoti R. , Luceri V. , Bianco G.
Published: October 2002

Long wavelength time variations of the gravity field detected by means of laser tracking of geodetic satellites provide nowadays the unique opportunity to infer simultaneously the upper and lower mantle viscosity and the mass imbalance between ice accumulation and loss in Antarctica and Greenland. Here we show that mantle viscosity inversion based on stratified viscoelastic Earth models of the Pleistocene deglaciation, on two independent Satellite Laser Ranging (SLR) solutions for the even and odd zonal components of the geopotential and on True Polar Wander (TPW), indicate that present day ice mass loss in Antarctica amounts to about −250 Gt/yr, equivalent to a global sea level rise of 0.7 mm/yr, and that the lower mantle is more viscous than the upper mantle. The odd zonals of the two SLR solutions and TPW indicate two admissible upper mantle viscosities, close to 1020 Pa s and to 1021 Pa s respectively.
Scaling of displacement spectra of near‐fault seismograms of the 1999 Chi‐Chi, Taiwan, earthquake
Authors: Huang Ming‐Wey , Wang Jeen‐Hwa
Published: October 2002

We study the scaling law of the displacement spectra, P(ω), which relates to ω in the form of P(ω) ∼ ω−β, from the seismograms, generated by the 1999 Chi‐Chi, Taiwan, earthquake, recorded at nine near‐fault stations. The values of corner frequency fc for the nine stations are almost 0.2 Hz. The pattern of the displacement spectrum at each station is similar to the theoretical one [cf. Aki, 1967]. When f < 0.2 Hz, the spectral amplitude is almost constant, and when f > 3 Hz, the spectral amplitude decays at a higher decreasing rate. When 0.2 Hz ≤ f ≤ 3 Hz, a power‐law scaling relation exists between P(ω) and ω. The estimated values of β for the nine stations vary from 1.63 to 3.04 and decrease from north to south. Such a variation might be mainly due to source effect.
Geomagnetic disturbances and their relationship to Interplanetary shock parameters
Authors: Jurac S. , Kasper J. C. , Richardson J. D. , Lazarus A. J.
Published: October 2002

We identify 107 fast, forward‐propagating interplanetary shocks observed by the Wind spacecraft from 1995–2000 to examine the influence of shock parameters on geomagnetic disturbances following the shock arrival at Earth. We find that the angle between the shock front normal and the interplanetary magnetic field (IMF) direction might play a useful role in forecasting the severity of geomagnetic storms occurring within 48 hours from the shock passage. Quasi‐perpendicular shocks, i.e. those nearly orthogonal to the IMF direction, constrain IMF components in the plane parallel to the shock front, making it more likely to produce southward IMF. We demonstrate that, regardless of the shock driver, about 40% of forward IP shocks result in intense magnetic storms when the shock normal is almost perpendicular to the IMF, compared to about 10–15% of shocks with normals not perpendicular to the IMF direction.
Partial recovery of the Arctic Ocean halocline
Authors: Boyd Timothy J. , Steele Michael , Muench Robin D. , Gunn John T.
Published: October 2002

The evolution during the 1990's of the cold halocline layer (CHL) of the Arctic Ocean is investigated using data from icebreaker and SCICEX submarine cruises. The CHL disappearance and subsequent partial recovery is described along repeated transects through the central Arctic Ocean from the Alpha Ridge to the Nansen Basin. Salinity at the top of the halocline is used as a measure of halocline development, with high salinity corresponding to a poorly developed halocline. In the Nansen, Amundsen, and Makarov basins, upper ocean salinity increased from 1991 to 1998 as the CHL disappeared, then decreased from 1998 to 2000 as it recovered. Salinity was higher over the study region through the 1990's than at any time during the prior 40 year period, hence the 1990's CHL recovery was only partial. Disappearance of the CHL from the Eurasian Basin in the early 1990's was due to a shift from the Laptev to East Siberian seas of the region for seaward flow of low salinity Siberian shelf waters. Ice velocities and sea level pressure fields suggest that the reappearance of the CHL in 1999 corresponded to a shift of this flow back to the Laptev Sea region.
Indirect climate forcing over the western US from Asian dust storms
Authors: Sassen Kenneth
Published: October 2002

Aerosols lofted to high altitudes by springtime Asian dust storms advect across the Pacific Ocean and, as recognized in recent years, regularly reach the western US. As part of our long‐term cirrus cloud research program using remote sensing measurements, we have observed unusually warm cirrus ice clouds associated with transported Asian dust aerosols. The polarization lidar data presented for illustration here suggest that the dust particles, which are indicated to be especially active ice nuclei, can affect the formation and phase of clouds, and hence alter their radiative properties at least as far away as the eastern Great Basin of the US.
Is desert dust making oligotrophic waters greener?
Authors: Claustre H. , Morel A. , Hooker S. B. , Babin M. , Antoine D. , Oubelkheir K. , Bricaud A. , Leblanc K. , Quéguiner B. , Maritorena S.
Published: October 2002

In situ optical measurements provide evidence that oligotrophic waters of the Mediterranean Sea have a greener color than would result from their phytoplankton content alone. This anomaly, detectable in low chlorophyll waters, remains unnoticed in the chlorophyll‐rich waters of the nearby waters of the Moroccan upwelling zone. It is due to enhanced absorption in the blue and enhanced backscattering in the green parts of the visible spectrum likely resulting from the presence of submicron Saharan dust in suspension within the upper layer. This result implies that regional estimations of carbon fixation from ocean color images might be significantly overestimated, not only in the Mediterranean Sea, but also in other oligotrophic areas of the Northern hemisphere, subjected to desert dust deposition.
The electric moho underneath Eastern Indian Craton
Authors: Bhattacharya Bimalendu B. , Shalivahan
Published: October 2002

Moho boundary, discovered about a century back, is well established on the basis of seismological studies. Electromagnetic studies using very low frequencies, however, have not been able to establish this boundary due to the presence of highly conducting continental lower crust. Magnetotelluric lithospheric study over the Eastern Indian Craton (3.3 Gyr) resolves the lower crust and upper mantle boundary due to the absence of highly conducting continental lower crust underneath the craton. From the present study it can be speculated that a dynamics other than the plate tectonics possibly existed up to the mid‐Archaean.
Vortex shedding and sediment resuspension associated with the interaction of an internal solitary wave and the bottom boundary layer
Authors: Stastna Marek , Lamb Kevin G.
Published: October 2002

In this note we present results on the interaction of fully nonlinear internal solitary waves with the oceanic bottom boundary layer. We show that for fully nonlinear solitary waves it is the interaction of the wave induced velocity field with the upstream boundary layer vorticity that leads to a vortex shedding instability beneath the wave. The vortex shedding provides an efficient mechanism for transporting sediment out of the bottom boundary layer. Bottom boundary stress profiles suggest that the vortex shedding can lead to the resuspension of sediment. In contrast to past studies we find that neither a separation bubble or a wave with a recirculating region are required for vortex shedding to occur.
Reconciling observations of global temperature change
Authors: Lindzen Richard S. , Giannitsis Constantine
Published: October 2002

It is suggested that the much publicized discrepancy between observed surface global mean temperature and global mean atmospheric temperature from 1979 to the present may be due to the fact that the atmosphere underwent a jump in temperature in 1976 (before the satellite temperature series began), and that the surface response was delayed for about a decade due to the ocean heat capacity. The ocean delay depends on both climate sensitivity and vertical heat transport within the ocean. It is shown that the observed delay is best simulated when sensitivity to doubling of CO2 is less than about 1C.
Ocean color observations of eddies during the summer in the Gulf of California
Authors: Pegau W. Scott , Boss Emmanuel , Martínez Antonio
Published: October 2002

Using SeaWiFS ocean color satellite images collected during 1997–2001, a series of eddies have been observed in the Gulf of California. These eddies are not clearly seen in the summertime sea surface temperature images. The surface circulation between the midriff islands and the mouth of the gulf appears to be dominated by this series of eddies that have an alternating sense of rotation. An eddy pair is observed to extend from Cabo Lobos in each of the three years, suggesting that the eddies are topographically locked. The formation mechanism of the eddies remains unknown; however, we suspect the most likely mechanism includes baroclinic instabilities along the coast produced by interactions between coastally trapped waves, and local wind driven currents.
Modes of high‐latitude electric field variability derived from DE‐2 measurements: Empirical Orthogonal Function (EOF) analysis
Authors: Matsuo Tomoko , Richmond Arthur D. , Nychka Douglas W.
Published: October 2002

In this study we characterize dominant modes of high‐latitude electric field variability as a set of two‐dimensional empirical orthogonal functions (EOFs), based on a sequential non‐linear regression analysis of the electric field derived from plasma drift measurements during the Dynamics Explorer‐2 (DE‐2) satellite mission (1981–1983). Together with the mean fields, 11 EOFs are capable of representing 68% of the squared electric field in the original data, leaving only a fairly random component as a residual. While such mathematically independent EOFs do not necessarily represent physically independent modes of variability, each of the first two EOFs is actually related to a widely known physically prominent effect on the convection patterns. Variability associated with the interplanetary magnetic field (IMF) BY component emerges as the primary mode, and variability associated with the IMF BZ effect emerges as the secondary mode. The tertiary mode reflects variability in the cusp region, but is not significantly correlated with the IMF.
Particle bursts in the Jovian magnetosphere: Evidence for a near‐Jupiter neutral line
Authors: Woch Joachim , Krupp Norbert , Lagg Andreas
Published: October 2002

In the magnetosphere of Jupiter the plasma convection is driven by the planetary rotation up to considerable distances from the planet. However, at larger distances the rotational flow is often disrupted by explosive events, seen as jets of energetic particles propagating in the radial direction. These events are observed very frequently and can be regarded as an intrinsic property of the Jovian system. A statistical survey shows that the burst events are concentrated in the post‐midnight tail region. Inward directed bursts dominate closer to the planet, outward directed bursts further away from the planet. The transition from mainly inward to mainly outward directed bursts defines the most probable location of a near‐Jupiter neutral line. The findings corroborate early models which postulate that magnetic flux tubes heavily loaded with plasma originating from the moon Io will be stretched by the centrifugal forces up to such a degree that spontaneous reconnection sets in. This leads to acceleration of plasma and the release of plasmoids into interplanetary space. The process may also drive the recently observed auroral dawn storms at Jupiter.
The indirect aerosol effect over Europe
Authors: Krüger Olaf , Graßl Hartmut
Published: October 2002

In order to assess the influence of anthropogenic emissions on cloud albedo over Europe a reprocessed set of satellite measurements from 1985 to 1999 was investigated. Special emphasis was given to the Central European main emission area, including the so‐called ‘Black Triangle’ which covered parts of Germany, the Czech Republic and Poland. Due to the decrease of aerosol precursor gases the analysis reveals a pronounced decrease of cloud albedo of about 2% from the late 80s to the late 90s. During winter in source regions of anthropogenic particulate matter emissions the cloud reflectance is more than 5% lower referring in addition to an absorption effect caused by black carbon in clouds. The comparison with emission data as well as model results of long range transport over Europe strongly supports the conclusion that the changed indirect aerosol effect is responsible for significantly changed cloud optical properties. Radiative transfer calculations indicate for the classical Twomey effect a change in radiative forcing of about 1.5 W/m2 from the late 80s to the late 90s. In addition during winter a radiative forcing of about 3 W/m2 due to the absorption effect for both the late 80s and the late 90s is estimated.
Rheological control of subcrustal seismicity in the Apennines subduction (Italy)
Authors: Carminati Eugenio , Giardina Francesca , Doglioni Carlo
Published: October 2002

Different rheological behavior of continental vs oceanic lithosphere can account for the shallower and lower subcrustal seismicity below the northern Apennines with respect to the deeper and more intense seismicity below the Calabrian arc in the south along the same subduction zone. We show that, for equal temperature distribution, oceanic slabs are predicted to display brittle behavior down to depths higher than those predicted for a continental slab. This opposite rheology is likely amplified by the higher strain rates and cooler slab temperatures in the south due to the faster subduction rollback and the oceanic composition of the downgoing lithosphere. Therefore the paucity of seismicity in the central‐northern Apennines might not be related to the absence of the slab, but rather to its continental nature and to lower strain rates.
ESR mapping of polar‐cap patches in the dark cusp
Authors: Carlson H. C. , Oksavik K. , Moen J. , van Eyken A. P. , Guio P.
Published: October 2002

We present the first ever measurement of the full thermal plasma properties, of an ionospheric patch in full darkness in the noon region where patches are believed to form. Further these data present the first experimental evidence for the Lockwood and Carlson class of mechanisms for forming patches by plasma injection. These data were possible only because of a new measurement capability we had to develop. We introduce the capability here because it crosses the high‐speed threshold that now allows study of a broader class of mesoscale plasma flow‐transients, which are thought to occur over time scales near 2 minutes vice 8–10 minutes. Cumulatively such transients may significantly drive global convection. We demonstrate both the validity of and need for our new measurement capability, by presenting a transient flow reversal sweeping across a 500 by 1000 km area, with initial reversal in 4 minutes, and recovery within 6 minutes.
Seismological evidence for a sub‐volcanic arc mantle wedge beneath the Denali volcanic gap, Alaska
Authors: McNamara Daniel E. , Pasyanos Michael E.
Published: October 2002

Arc volcanism in Alaska is strongly correlated with the 100 km depth contour of the western Aluetian Wadati‐Benioff zone. Above the eastern portion of the Wadati‐Benioff zone however, there is a distinct lack of volcanism (the Denali volcanic gap). We observe high Poisson's ratio values (0.29–0.33) over the entire length of the Alaskan subduction zone mantle wedge based on regional variations of Pn and Sn velocities. High Poisson's ratios at this depth (40–70 km), adjacent to the subducting slab, are attributed to melting of mantle‐wedge peridotites, caused by fluids liberated from the subducting oceanic crust and sediments. Observations of high values of Poisson's ratio, beneath the Denali volcanic gap suggest that the mantle wedge contains melted material that is unable to reach the surface. We suggest that its inability to migrate through the overlying crust is due to increased compression in the crust at the northern apex of the curved Denali fault.
Renewal of the bottom water after the winter 2000–2001 may spin‐up the thermohaline circulation in the Japan Sea
Authors: Senjyu Tomoharu , Aramaki Takafumi , Otosaka Shigeyoshi , Togawa Orihiko , Danchenkov Mikhail , Karasev Eugeny , Volkov Yuri
Published: October 2002

The newly formed bottom water in the Japan Sea was observed in the summer of 2001 after the severe winter 2000–2001. The new bottom water, which was observed in the northwestern Japan Sea, showed low temperature, high salinity, high dissolved oxygen and low nutrients concentration compared to the old bottom water. The distribution of the new bottom water indicates that the bottom water was formed in the south off Vladivostok, not in the northern Japan Sea north of 43°N, and was advected to the observation area. It is suggested that the formation event occurred in the late January‐early February 2001, because strong flows of faster than 8 cms−1 appeared abruptly from mid‐February 2001. This formation event may contribute not only the relaxation of the oxygen‐decreasing trend in the bottom layer but also the spin‐up of the thermohaline circulation in the Japan Sea.
Upper mesosphere summer echoes detected with the Antarctic Syowa HF radar
Authors: Ogawa Tadahiko , Nishitani Nozomu , Sato Natsuo , Yamagishi Hisao , Yukimatu Akira S.
Published: October 2002

Peculiar HF radar echoes observed at Syowa Station, Antarctica (69.0°S, 39.6°E) are reported. The echoes occurred in summer at slant ranges between 180 (first range gate) and 315 km under very quiet geomagnetic conditions. They are characterized by a duration of less than 80 min, quasi—periodic oscillations of velocity and echo power with periods of 5–20 min, velocities between −40 and +20 ms−1, and narrow spectral widths less than 40 ms−1. From data of June, July, December 1997, and January 1998, we identified such echoes on 4 days in December and January (summer) but not in June and July (winter). Although range resolution of the HF radar (45 km) is very poor, we believe that our echoes are Antarctic Polar Mesosphere Summer Echoes (PMSE), relying on that the echo characteristics are very similar to the Arctic PMSE.
Relating MODIS‐derived surface albedo to soils and rock types over Northern Africa and the Arabian peninsula
Authors: Tsvetsinskaya Elena A. , Schaaf C. B. , Gao F. , Strahler A. H. , Dickinson R. E. , Zeng X. , Lucht W.
Published: October 2002

We use the MODerate resolution Imaging Spectroradiometer (MODIS) aboard the Terra spacecraft to derive surface albedo for the arid areas of Northern Africa and the Arabian peninsula. Albedo in seven MODIS spectral bands for land and three broad bands (for shortwave, near infrared, and visible portions of the spectrum) is produced. Surface albedo is derived from MODIS observations during a sixteen‐day period and is analyzed at 1 km spatial resolution. MODIS data show considerable spatial variability of surface albedo in the study region that is related to soil and geological characteristics of the surface. For example, solar shortwave white‐sky albedo varies by a factor of about 2.5 from the darkest volcanic terrains to the brightest sand sheets. Vegetation contribution to surface reflectance is essentially negligible since we only considered pixels with under 10 percent fractional canopy cover. Few, if any, coupled land‐atmosphere global or regional models capture this observed spatial variability in surface reflectance or albedo. Here we suggest a scheme that relates soil groups (based on the United Nations Food and Agriculture Organization, FAO, soil classification) and rock types (based on the United States Geological Survey, USGS, geological maps) to MODIS derived surface albedo statistics. This approach is a first step towards the incorporation of the observed spatial variability in surface reflective properties into climate models.
First measurement of atmospheric density and pressure by meteor diffusion coefficient and airglow OH temperature in the mesopause region
Authors: Takahashi H. , Nakamura T. , Tsuda T. , Buriti R. A. , Gobbi D.
Published: October 2002

Atmospheric density and pressure in the mesopause region, around 87 km, are inferred using meteor trail ambipolar diffusion coefficient, D, and simultaneously observed airglow OH rotational temperature, TOH. This is the first time to determine the atmospheric density, temperature and pressure by this method. From the 17 nights of data, we found that the number density at around 87 km of altitude varied from 0.9 to 1.2 × 1014 cm−3, and the pressure varied from 0.27 to 0.35 Pascal. The density variation is opposite to the temperature. The OH (6,2) band emission rates showed negative correlation with the density, contrast to positive relation with the temperature. In order to explain temporal variation of the OH emission rate, therefore, it is necessary to assume change of atomic oxygen mixing ratio in the emission heights.
Crustal resistivity structure at 9°50′N on the East Pacific Rise: Results of an electromagnetic survey
Authors: Evans Rob L. , Webb Spahr C. , Crawford W. , Golden C. , Key K. , Lewis L. , Miyano H. , Roosen E. , Doherty D. ,   RIFT‐UMC Team
Published: October 2002

We report the first results of an extensive electromagnetic survey of the East Pacific Rise (EPR) at 9°50′N, which used the magnetometric resistivity (MMR) technique to measure the electrical resistivity structure of the seafloor in the vicinity of the spreading center. Ten seafloor magnetometers were deployed in areas of known hydrothermal activity, in axial sites devoid of venting, and further off‐axis to a distance of approximately 4 km. Data collected at off‐axis sites show higher seafloor resistivities than at axial sites. This response is opposite to that expected from porosity controlled resistivity structure, with a thicker high‐porosity extrusive layer 2A off‐axis, as required by seismic data. An explanation for the reduced axial resistivities is that the uppermost few hundred meters of crust are much hotter beneath the ridge crest than a few kilometers off‐axis, lowering the pore‐fluid resistivity.
Turn‐on of 2–3 kHz radiation beyond the heliopause
Authors: Cairns Iver H. , Zank G. P.
Published: October 2002

The Voyager spacecraft observe radio emissions near 2–3 kHz that appear to be generated when an interplanetary shock nears the heliopause. This paper presents a detailed, qualitative theory for where and why the radiation turns on. The radiation turns on just beyond the heliopause due to the shock moving into a region primed with a strong superthermal electron tail. Lower‐hybrid drive produces the tail: ambient electrons are resonantly accelerated by lower hybrid waves driven by a ring‐beam instability of pickup protons. The pickup protons originate as neutrals in the inner heliosheath. Strong arguments suggest that the tail exists only beyond the heliopause (within ≈ 20–50 AU of the nose) and that shock acceleration of the tail dramatically enhances the foreshock electron beams, Langmuir waves and radiation, so that the shock triggers observable radiation only when beyond the heliopause.
Biogeochemical patchiness at the sea surface
Authors: Mahadevan A. , Campbell J. W.
Published: October 2002

The surface distributions of many tracers in the ocean are highly correlated in time and space on meso (∼100 km) and smaller scales (Figure 1). However, their characteristic scales of variability differ. Some variables like sea surface chlorophyll (Chl) are very fine‐scaled or patchy, while others like sea surface temperature (SST) are not. We characterize the patchiness of a distribution quantitatively by the dependence of the variance V on the length scale L as V ∼ Lp; smaller p corresponds to greater patchiness. Using scaling and a numerical model we show that patchiness, p, varies with the characteristic response time τ of the tracer to processes that alter its concentration in the upper ocean as p ∼ log τ. This suggests that sea surface Chl is more patchy (has smaller p) than SST at mesoscales because the characteristic time scale of phytoplankton growth in response to the availability of nutrients is less than that for the equilibration of temperature in response to heat fluxes. Similarly, sea surface dissolved oxygen (O2) exhibits more fine‐scaled variability than total dissolved inorganic carbon (TCO2) because O2 equilibrates with the atmosphere much more rapidly than TCO2. Tracers that are more patchy require higher resolution to model and sample; the sampling or model grid spacing required scales as exp(−1/log τ). The quantitative relationship between p and τ can be used to relate various biogeochemical distributions, particularly to those that are remotely sensed, and to deduce biogeochemical response times of various tracers or plankton species from the characteristics of their distributions in space or time.
Magnetotelluric imaging of the creeping segment of the San Andreas Fault near Hollister
Authors: Bedrosian Paul A. , Unsworth Martyn J. , Egbert Gary
Published: October 2002

Fluids may play a significant role in the earthquake rupture process. Since fluids can dramatically change the electrical resistivity of crustal rocks, electromagnetic exploration methods can image in situ fault‐zone fluids. Magnetotelluric (MT) data has been collected on segments of the San Andreas Fault (SAF) in Central California exhibiting a range of seismic behavior from locked to creeping. This paper describes MT data from the creeping segment of the SAF near Hollister, California. Inversion models image a zone of enhanced conductivity beneath the surface trace of the SAF that has similar geometry and greater depth extent than the fault zone conductor at Parkfield. Comparison with geologic and seismic tomographic studies show this zone is bounded by the San Andreas and Calaveras Faults, and coincident with a zone of low seismic P‐wave velocities. Combined with previous MT studies, this indicates a correlation between seismicity and the presence of fault‐zone fluids.
The dynamical foundation of fractal stream chemistry: The origin of extremely long retention times
Authors: Scher Harvey , Margolin Gennady , Metzler Ralf , Klafter Joseph , Berkowitz Brian
Published: October 2002

We present a physical model to explain the behavior of long‐term, time series measurements of chloride, a natural passive tracer, in rainfall and runoff in catchments [Kirchner et al., Nature, 403(524), 2000]. A spectral analysis of the data shows the chloride concentrations in rainfall to have a white noise spectrum, while in streamflow, the spectrum exhibits a fractal 1/f scaling. The empirically derived distribution of tracer travel times h(t) follows a power‐law, indicating low‐level contaminant delivery to streams for a very long time. Our transport model is based on a continuous time random walk (CTRW) with an event time distribution governed by ψ(t) ∼ Aβt−1−β. The CTRW using this power‐law ψ(t) (with 0 < β < 1) is interchangeable with the time‐fractional advection‐dispersion equation (FADE) and has accounted for the universal phenomenon of anomalous transport in a broad range of disordered and complex systems. In the current application, the events can be realized as transit times on portions of the catchment network. The travel time distribution is the first passage time distribution F(t;l) at a distance l from a pulse input (at t = 0) at the origin. We show that the empirical h(t) is the catchment areal composite of F(t;l) and that the fractal 1/f spectral response found in many catchments is an example of the larger class of transport phenomena cited above. The physical basis of ψ(t), which determines F(t;l), is the origin of the extremely long chemical retention times in catchments.
How does the ionospheric rotational Hall current absorb the increasing energy from the field‐aligned current system?
Authors: Yoshikawa Akimasa
Published: October 2002

It has been well recognized that field‐aligned current (FAC) systems lose their energy in the ionosphere through the Joule dissipation that is caused by their closure via the ionospheric Pedersen current, and that the ionospheric Hall current cannot contribute the total energy dissipation. However, it is also true that the rotational Hall current is excited by the incident FAC, and it radiates a Poynting vector that grows a poloidal‐type magnetic field. Even if the Hall effect cannot do work on an external system, what does its contribution to the accumulation of poloidal magnetic energy really mean? In this paper, it is clarified that the divergent Hall current, excited during the transient phase of magnetosphere‐ionosphere coupling, closes via the FAC and produces a Hall current generator, which pumps up the energy of the FAC system to increase the ionospheric rotational Hall current (together with its associated poloidal magnetic field).