bluuebunny/crossref_metadata_2025 huggingface dataset:
Major pathways of Atlantic water in the northern North Atlantic and Nordic Seas toward Arctic
Authors: Orvik Kjell Arild , Niiler Peter
Published: October 2002

The major pathways of near‐surface Atlantic water in the northern North Atlantic and Nordic Seas are identified as current speeds above 30 cm/s, using 1014 Lagrangian drifters combined with previously published hydrography. The inflow over the Scotland‐Greenland ridge and establishment of the two‐branch Norwegian Atlantic Current (NwAC) are described in light of the circulation in the northern North Atlantic. The western branch of the NwAC appears as a jet in the Polar Front, topographically guided from the Iceland‐Faroe Front, through the Nordic Seas toward Fram Strait. The eastern branch starts as a shelf edge current above the Irish‐Scottish continental shelf, and after passing through the Faroe‐Shetland Channel, it continues northward along the Norwegian shelf edge toward the Arctic, with a branch bifurcating into the Barents Sea. The NwAC appears to maintain its two‐branch structure throughout the Nordic Seas, with the Atlantic water confined to a 200–600 km wide wedge.
A process for low‐temperature olivine‐spinel transition under quasi‐hydrostatic stress
Authors: Raterron Paul , Chen Jiuhua , Weidner Donald J.
Published: October 2002

The behavior of fayalite—the Fe2SiO4 olivine end‐member (Fa100)—has been monitored during high‐pressure and low‐temperature experiments using in‐situ x‐ray synchrotron radiation, in order to investigate the effect of stress on the olivine (α‐phase)—spinel (γ‐phase, or ringwoodite) transition. The run products were investigated by optical and transmission electron microscopy (TEM). A low‐temperature mechanism for the α‐γ transformation is documented. This shear induced mechanism is operative in hydrostatically compressed samples at temperature as low as 450°C, and is driven by the shear stress generated by the volume change of the transformation itself. Projection to mantle compositions suggests that metastable subduction of olivine will not occur in the deep transition zone.
Near IR photolysis of HO2NO2: Implications for HOx
Authors: Salawitch Ross J. , Wennberg Paul O. , Toon Geoffrey C. , Sen Bhaswar , Blavier Jean‐Francois
Published: October 2002

We report observations and calculations of peroxynitric acid, HO2NO2, in the stratosphere and upper troposphere. The simulations show that photolysis of HO2NO2 via excitation of purely vibrational modes at wavelengths longward of 760 nm (the near IR) can dominate loss of this species. Consideration of this photolytic pathway reduces calculated HO2NO2, resolving a large discrepancy between standard model calculations and observations of HO2NO2 at high‐latitude spring. The lower calculated abundance of HO2NO2 reduces the efficiency of the OH + HO2NO2 sink of HOx. Consideration of this process leads to large increases in calculated HOx (20 to 60%) for high‐latitude spring and better agreement with observed stratospheric abundances of HOx. Near IR photolysis of HO2NO2 alters the coupling between NOx and HOx in stratospheric and upper tropospheric photochemical models.
Proton aurora dynamics in response to the IMF and solar wind variations
Authors: Chang S.‐W. , Mende S. B. , Frey H. U. , Gallagher D. L. , Lepping R. P.
Published: October 2002

On May 23, 2000, proton auroras observed by IMAGE FUV on the dayside were very dynamic. Auroral pattern at the cusp footpoint is well correlated with IMF and solar wind parameters. A proton aurora brightened at high latitude poleward from the dayside oval after solar wind ion temperature increased while solar wind density and bulk speed were steady. It then vanished after IMF turned southward. Under this IMF condition, auroral activity occurred only in the dayside oval. As IMF Bz reverted to northward, cusp proton aurora reappeared at high latitude. The location of the cusp proton aurora changes with the IMF By polarity, consistent with previous reports. These results suggest an upstream source for the observed high‐latitude cusp proton aurora. One possible explanation is that bow shock energetic ions are transported into the cusp via the high‐latitude magnetic merging process to induce optical emissions in the ionosphere.
S, Cl and F degassing as an indicator of volcanic dynamics: The 2001 eruption of Mount Etna
Authors: Aiuppa Alessandro , Federico Cinzia , Paonita Antonio , Pecoraino Giovannella , Valenza Mariano
Published: October 2002

The recent eruption of Mount Etna (July 2001) offered the opportunity to analyze magma‐derived volatiles emitted during pre‐ and syn‐eruptive phases, and to verify whether their composition is affected by changes in volcanic dynamics. This paper presents the results of analyses of F, Cl and S in the volcanic plume collected by filter‐packs, and interprets variations in the composition based on contrasting solubility in magmas. A Rayleigh‐type degassing mechanism was used to fit the acquired data and to estimate Henry's solubility constant ratios in Etnean basalt. This model provided insights into the dynamics of the volcano. Abundances of sulfur and halogens in eruptive plumes may help predict the temporal evolution of an ongoing effusive eruption.
Cosmic ray‐induced aerosol‐formation: First observational evidence from aircraft‐based ion mass spectrometer measurements in the upper troposphere
Authors: Eichkorn S. , Wilhelm S. , Aufmhoff H. , Wohlfrom K. H. , Arnold F.
Published: October 2002

Large positive cluster ions with atomic mass numbers up to 2500 have for the first time been detected in the upper troposphere using an aircraft‐based large ion mass spectrometer (LIOMAS). Three ion families seem to be present (types 1, 2 and 3). Type 1 ions probably are H+BbWw (W is H2O and B is mostly acetone (CH3)2CO, and b ≤ 2). Type 2 ions are probably H+BbAaWw (A = H2SO4) formed by A‐attachment to type 1 ions. Type 3 ions are probably very small charged aerosols formed preferably by type 1 ion attachment to stable electrically neutral AxWy clusters. The latter are preferably formed by ion‐ion recombination. Hence our observations provide strong evidence for the ion‐mediated formation and growth of aerosol particles in the upper troposphere.
Surface electric variations induced by deep hydraulic stimulation: An example from the Soultz HDR site
Authors: Marquis Guy , Darnet Mathieu , Sailhac Pascal , Singh A. K. , Gérard André
Published: October 2002

We carried out monitoring of surface electric potential variations at the Soultz Hot Dry Rock site (France) during a stimulation experiment where 23 000 m3 of water were injected in granite at 5 km depth. We have observed a long‐period (9–10 days) potential variation with a maximum amplitude of ≈5 mV, thanks to the conductive well casing. The start of this anomalous potential coincides with that of the water injection and its magnitude increases as more water is injected before returning toward its original value after shut‐in. We interpret this anomalous potential as an electrokinetic effect which is caused by the injection of water circulating in deep fractures. We modeled the pressure distribution during the stimulation and obtained the surface SP using electrokinetic coupling relationships. We found that an in‐situ coupling coefficient of ≈−1 mV/MPa, at the low end of laboratory values, gives a good fit to the data.
Ground‐coupled air waves and diffracted infrasound from the Arequipa earthquake of June 23, 2001
Authors: Le Pichon A. , Guilbert J. , Vega A. , Garcés M. , Brachet N.
Published: October 2002

On June 23, 2001, a strong earthquake measuring Mw 8.4 occurred along the coast of south‐central Peru. Coherent infrasonic waves were detected over a period of one hour by the IS08 infrasound station in Bolivia. Analysis of the ground‐coupled air waves shows that the rupture propagated from the northwestern to the southeastern part of the fault with a rupture velocity of 3.3 km/s. The azimuth variation of the infrasonic waves is attributed to a distribution of secondary sources along the highest mountain ranges, which excite infrasonic waves that are diffracted to the ground. The predominant source of infrasound is likely distributed along the Andean Cordillera. Using the azimuth and arrival time determination, the horizontal scale size of the distant source regions of infrasonic waves is reconstructed over distances greater than 400 km.
Recent lengthening of the south Asian summer monsoon season
Authors: Syroka Joanna , Toumi Ralf
Published: October 2002

An increase in October precipitation since 1979 over the south Asian region has been observed. This increase is found to be associated with enhanced cross‐equatorial flow and strengthened cyclonic circulation over the Indian subcontinent synonymous with a northwest shift in the tropical convergence zone. We show that October lower tropospheric flow is becoming more like September circulation, indicating an increasing delay in the retreat phase of the monsoon system. This extension of the south Asian summer monsoon may be linked to enhanced land‐sea contrast.
A high‐quality global gravity field model from CHAMP GPS tracking data and accelerometry (EIGEN‐1S)
Authors: Reigber Christoph , Balmino Georges , Schwintzer Peter , Biancale Richard , Bode Albert , Lemoine Jean‐Michel , König Rolf , Loyer Sylvain , Neumayer Hans , Marty Jean‐Charles , Barthelmes Franz , Perosanz Felix , Zhu Shen Yuan
Published: October 2002

Using three months of GPS satellite‐to‐satellite tracking and accelerometer data of the CHAMP satellite mission, a new long‐wavelength global gravity field model, called EIGEN‐1S, has been prepared in a joint German‐French effort. The solution is derived solely from analysis of satellite orbit perturbations, i.e. independent of oceanic and continental surface gravity data. EIGEN‐1S results in a geoid with an approximation error of about 20 cm in terms of 5 × 5 degree block mean values, which is an improvement of more than a factor of 2 compared to pre‐CHAMP satellite‐only gravity field models. This impressive progress is a result of CHAMP's tailored orbit characteristics and dedicated instrumentation, providing continuous tracking and direct on‐orbit measurements of non‐gravitational satellite accelerations.
Ionospheric signatures of plasmaspheric tails
Authors: Foster J. C. , Erickson P. J. , Coster A. J. , Goldstein J. , Rich F. J.
Published: October 2002

We make direct comparisons between GPS maps of total electron content (TEC) over the North American continent, Millstone Hill radar observations of storm enhanced density, and low and high‐altitude satellite measurements of the perturbation of the outer plasmasphere during the March 31, 2001 geomagnetic storm. We find that storm enhanced density (SED) and plumes of greatly‐elevated TEC are associated with the erosion of the outer plasmasphere by strong sub‐auroral polarization electric fields. The SED/TEC plumes identified at low altitude map closely onto the magnetospheric determination of the boundaries of the plasmapause and plasmaspheric tail determined by EUV imaging from the IMAGE spacecraft. Characteristics of the SED/TEC plumes/tails for the March 31, 2001 event are: TEC ∼ 100 TECu; F‐region sunward velocity ∼1000 m/s; sunward flux ∼5*1024 ions s−1; total transport to dayside magnetopause/merging region (3‐hr event) ∼5*1028 ions.
LIDAR measurements of cirrus clouds in the northern and southern midlatitudes during INCA (55°N, 53°S): A comparative study
Authors: Immler Franz , Schrems Otto
Published: October 2002

Cirrus clouds have been probed at two locations in the midlatitudes of the southern (SH) and northern hemisphere (NH) with a Mobile Raman Aerosol Lidar (MARL) as part of the European INCA field experiments in 2000. MARL offers the opportunity to observe visible and subvisible clouds and to determine the optical depth τ in a range from below 10−3 up to 3. Despite different synoptic conditions we find at both locations similar macrophysical cloud properties, like mean base and top temperature among others. The frequencies of the optical depth show a characteristic distribution with a high share of subvisible clouds at both locations. While thin haze layers are frequently detected in the NH alone, we find highly depolarizing cirrus clouds only in the SH. These differences indicate that different cirrus properties and formation mechanisms are present at the two sites.
Adsorption isotherms of acetone on ice between 193 and 213 K
Authors: Dominé Florent , Rey‐Hanot Laurence
Published: October 2002

The adsorption isotherms of acetone on ice were measured at 193, 203 and 213 K using a volumetric method with mass spectrometric detection. Henry's law applies for values of the acetone partial pressure, Pacetone, lower than 10−3 Pa. Where Henry's law applies, the number of acetone molecules adsorbed per cm2 of ice, is: nads = 90.53 × Pacetone × exp (6610.2/T), with Pacetone in Pa and T in K. The measured enthalpy of adsorption of acetone on ice is ΔHads = −55±7 kJ/mol. Acetone values previously measured in Arctic snow are too high to be due to adsorbed acetone. Acetone was then probably dissolved in ice or in organic aerosols contained in snow. Adsorption of acetone in the snowpack or on ice crystals in cirrus clouds is insufficient to affect Pacetone above the snow or in the clouds.
Iron‐Nickel alloy in the Earth's core
Authors: Lin Jung‐Fu , Heinz Dion L. , Campbell Andrew J. , Devine James M. , Mao Wendy L. , Shen Guoyin
Published: October 2002

The phase relations of an Fe10wt%Ni alloy were investigated in a diamond anvil cell up to 86 GPa and 2382 K. Adding nickel into iron stabilizes the fcc phase to higher pressures and lower temperatures compared to pure iron, and a region of two‐phase coexistence between fcc and hcp phases is observed. Iron with up to 10 wt% nickel is likely to be in the hcp structure under inner core conditions. The axial ratio (c/a) of hcp‐Fe10wt%Ni has a weak pressure dependence, but it increases substantially with increasing temperature. The extrapolated c/a ratio at ∼5700 K and ∼86 GPa is approximately 1.64, lower than a theoretically predicted value of nearly 1.7 for hcp‐Fe at 5700 K and inner‐core pressure. A lower c/a ratio should have an effect on the longitudinal anisotropy of the hcp phase, and hence, may influence the interpretation of the seismic wave anisotropy of the inner core.
Tidal pumping of groundwater into the coastal ocean revealed from submarine 222Rn and CH4 monitoring
Authors: Kim Guebuem , Hwang Dong‐Woon
Published: October 2002

There has emerged a recognition that the submarine discharge of fresh, brackish, and marine groundwaters into the coastal ocean is comparable to the inputs via river discharge. However, the factors controlling submarine groundwater discharge (SGD) are poorly understood owing to a lack of SGD measurement tools in dynamic coastal waters. We observed bi‐hourly variations of the natural SGD tracers, 222Rn and CH4, at a coastal seawater station over two seasons using novel monitoring techniques. This unique data set suggests that SGD increases sharply from neap to spring tide during the wet season. The observed increase is much greater than what would be expected from the rainfall and tidal‐height changes. We conclude from this that the temporal variation of SGD is regulated predominantly by a semi‐monthly fluctuation of a tidal oscillating pumping force in this environment.
On the evolution of the thermocline and subthermocline eastward currents in the Equatorial Atlantic
Authors: Bourlès B. , D'Orgeville M. , Eldin G. , Gouriou Y. , Chuchla R. , DuPenhoat Y. , Arnault S.
Published: October 2002

Eastward currents in the thermocline and subthermocline layers of the tropical Atlantic Ocean are described using observations obtained during two boreal summer cruises covering the whole equatorial basin. The analysis focuses on the eastward evolution of zonal currents in the thermocline and sub‐thermocline. The Equatorial Undercurrent is not found close to the African coast in boreal summer 2000, maybe because of interannual variability. As observed in the Pacific, the South and North Equatorial Undercurrents are shown to shift poleward from west to east, and the two cruises indicate that the North Equatorial Undercurrent does not enter the Gulf of Guinea. The South and North Intermediate Countercurrents are variable with longitude and, contrarily to the observations in the eastern equatorial Pacific, are not found in the east of the Guinea basin.
Simulation of ion velocity distributions in the magnetosheath
Authors: Lin Y. , Wang X. Y.
Published: October 2002

A two‐dimensional global hybrid simulation is carried out to study the ion velocity distributions in the dayside magnetosheath in the presence of a northward interplanetary magnetic field. In the simulation, the bow shock and the magnetosheath form self‐consistently by the interaction between the solar wind and the geomagnetic field. Downstream of the quasi‐perpendicular shock, the initial isotropic distribution of upstream ions first becomes an oval‐shaped bi‐Maxwellian distribution with the perpendicular temperature T⟂ greater than the parallel temperature T∥. These downstream ions are then found to evolve to a conic‐like or D‐shaped distribution in the high‐latitude magnetosheath prior to the transmission into the magnetosphere. The presence of the D‐shaped distribution is due to the adiabatic ion motion from the subsolar magnetosheath with a high magnetic field strength to high latitudes with a lower field, but not due to magnetic reconnection at the high‐latitude magnetopause.
‘Torus’ distribution of interstellar helium pickup ions: Direct observation
Authors: Oka M. , Terasawa T. , Noda H. , Saito Y. , Mukai T.
Published: October 2002

A‘torus’‐like velocity distribution of the helium pickup ions has been detected in interplanetary space by GEOTAIL. A statistical survey shows that the observation probability of the ‘torus’ distribution amounts to nearly 20% and that the distribution pattern depends on the local magnetic field directions and turbulence levels. These results support the recent finding of a low pitch angle scattering rate and a large mean free path.
Concentration and δD of molecular hydrogen in boreal forests: Ecosystem‐scale systematics of atmospheric H2
Authors: Rahn Thom , Eiler John M. , Kitchen Nami , Fessenden Julianna E. , Randerson James T.
Published: October 2002

We examined the concentration and δD of atmospheric H2 in a boreal forest in interior Alaska to investigate the systematics of high latitude soil uptake at ecosystem scale. Samples collected during nighttime inversions exhibited vigorous H2 uptake, with concentration negatively correlated with the concentration of CO2 (−0.8 to −1.2 ppb H2 per ppm CO2) and negatively correlated with δD of H2. We derived H2 deposition rates of between 2 to 12 nmol m−2 s−1. These rates are comparable to those observed in lower latitude ecosystems. We also derive an average fractionation factor, α = D:Hresidual/D:Hconsumed = 0.94 ± 0.01 and suggestive evidence that α depends on forest maturity. Our results show that high northern latitude soils are a significant sink of molecular hydrogen indicating that the record of atmospheric H2 may be sensitive to changes in climate and land use.
How sharp is the tropopause at midlatitudes?
Authors: Birner Thomas , Dörnbrack Andreas , Schumann Ulrich
Published: October 2002

Ten years of high‐resolution radiosonde data are contrasted with fifteen years of ECMWF reanalysis (ERA) data to explore the tropopause region above two midlatitude stations (Munich and Stuttgart) in Southern Germany. We present time‐averaged vertical profiles of several meteorological parameters relative to the tropopause. A strong mean inversion at the tropopause is evident from the radiosonde profiles with a vertical extension of about 2 km and a temperature increase of about 4 K. The impact of the tropopause definition on the strength of this inversion is discussed as well as the relevance of baroclinic eddies in forming it. The climatological profiles for Munich and Stuttgart do not differ significantly.
Acausal relations between topographic slope and drainage area
Authors: Schorghofer Norbert , Rothman Daniel H.
Published: October 2002

For real landscapes, the local slope is related to the area of the drainage basin. Such relations do not always indicate a causal link between drainage area and local slope. We provide a general and quantitative assessment of this statistical effect. Slope‐area relations in which slopes decay slower than roughly the cube root of drainage area are insensitive to processes that have shaped the landscape. To illustrate this point, surfaces unrelated to erosion are compared to real landscapes. The fluctuations of slope for constant drainage area provide a means of distinguishing between causal and random effects.
Cluster ions and ice particle nucleation: Positive feedback at the summer mesospause
Authors: Gumbel Jörg , Witt Georg
Published: October 2002

Large proton hydrate clusters H+(H2O)n can act as condensation nuclei for ice particles near the polar summer mesopause. However, laboratory data pose strong requirements on temperature and humidity for this nucleation mechanism to be feasible. Growth to sufficient cluster sizes is governed by competition between clustering reactions and recombination with free electrons. Since the abundance of free electrons can be strongly reduced by capture to ice particles, the presence of ice particles enhances the growth of cluster ions. This leads to a positive feedback mechanism with particle nucleation being favored in regions where particles already exist. Since this mechanism can amplify irregularities in the ionospheric particle and charge distribution, it is of potential interest for the understanding of polar mesosphere summer echoes (PMSE) and other layered phenomena. We demonstrate these ideas using a dusty ion‐chemical model of the D‐region.
The martian hydrosphere/cryosphere system: Implications of the absence of hydrologic activity at Lyot crater
Authors: Russell P. S. , Head J. W.
Published: October 2002

The Amazonian‐aged 215 km‐diameter Lyot crater represents a transient 'drill‐hole' into the martian hydrosphere/cryosphere system. Cratering mechanics predict that the event should have penetrated the cryosphere and released groundwater held under artesian conditions. A plausible explanation for the lack of evidence for hydrologic activity within Lyot is an absence of abundant subsurface groundwater in the region at the time of impact.
Efficient gravity field recovery using in situ disturbing potential observables from CHAMP
Authors: Han S.‐C. , Jekeli Christopher , Shum C. K.
Published: October 2002

We demonstrate an efficient method to determine gravity field model using data from accelerometer‐ and GPS‐equipped satellites, such as CHAMP. On the basis of the conservation of energy principle, in situ (on‐orbit) and along track disturbing potential observables were computed using 16‐days of CHAMP data. The global disturbing potential observables were then used to determine a 50 × 50 test gravity field solution (OSU02A) by employing a computationally efficient inversion technique based on conjugate gradient [Han et al., 2002]. An evaluation of the model using independent GPS/leveling heights and Arctic gravity data, and comparisons with existing gravity models, EGM96 and GRIM5C1, and new models, EIGEN1S and TEG4 which include CHAMP data, indicate that OSU02A is commensurate in geoid accuracy and, like other new models, it yields some improvement (10% better fit) in the polar region at wavelengths longer than 800 km.
Thermally induced lineations on the asteroid Eros: Evidence of orbit transfer
Authors: Dombard Andrew J. , Freed Andrew M.
Published: October 2002

Several systems of tectonic lineations have been observed on the surface of the asteroid 433 Eros. We suggest that many of these lineations may have resulted from thermal stresses associated with a secular change in surface temperature due to orbit migration. We demonstrate how thermal diffusion can lead to tectonic features and how such features should be oriented with respect to Eros' complex geometry. Comparison to observed lineations suggests that some may be explained by thermal stresses. Such stresses represent a largely unexplored tectonic process on asteroids and could be used to gain rare insight into chaotic orbital dynamics. If correct, our results imply a gross orbital history over the last ∼100 Myr involving slow (>several Myr), inward migration followed by more rapid, outward migration to its present orbit.
Convergence across the northwest Himalaya from GPS measurements
Authors: Banerjee P. , Bürgmann R.
Published: October 2002

Horizontal velocities of 26 Global Positioning System (GPS) stations in the northwest Himalayan region provide new constraints on the partitioning of India‐Eurasia convergence and elastic strain accumulation about the locked Main Frontal Thrust (MFT). The northwest‐striking Karakorum fault slips at 11 ± 4 mm/yr and contributes to east‐west extension of southern Tibet and westward motion of the northwest Himalaya towards Nanga Parbat, rather than playing a role in eastward extrusion of Tibet. Crustal shortening across the Himalaya occurs within a zone centered about 100 km north of the Siwalik Foothills and the MFT. Model inversions of the GPS data indicate that the MFT is locked over a width of ∼100 km. Comparison with geologic MFT‐slip‐rate estimates suggests that this zone is building up a slip deficit at a rate of 14 ± 1 mm/yr and will eventually fail in future great earthquakes.
The emission and chemistry of reactive nitrogen species in the plume of an Athena II solid‐fuel rocket motor
Authors: Popp P. J. , Ridley B. A. , Neuman J. A. , Avallone L. M. , Toohey D. W. , Zittel P. F. , Schmid O. , Herman R. L. , Gao R. S. , Northway M. J. , Holecek J. C. , Fahey D. W. , Thompson T. L. , Kelly K. K. , Walega J. G. , Grahek F. E. , Wilson J. C. , Ross M. N. , Danilin M. Y.
Published: October 2002

In situ measurements of NO, NOy, HNO3, ClO, CO2, H2O and particles were made in the plume of an Athena II solid‐fuel rocket motor (SRM) with instruments onboard the NASA WB‐57F high‐altitude aircraft. By normalization to CO2, the NOy emission index was calculated to be 2.7±0.6 g NO2 (kg fuel)−1. HNO3 is a significant and evolving component plume NOy. The principal source of HNO3 is thought to be the heterogeneous reaction between ClONO2 and HCl on emitted alumina particles. These measurements provide the first experimental evidence for the production of HNO3 and the activation of chlorine on SRM‐emitted alumina particles in the lower stratosphere.
Estimating peak currents at ground lightning impacts using remanent magnetization
Authors: Verrier V. , Rochette P.
Published: October 2002

The impact of lightning is permanently recorded in struck material by a secondary magnetization called “lightning induced remanent magnetization” (LIRM). We introduce an original rock magnetic method based on alternating field demagnetization to define both the geometry and the intensity of the peak lightning magnetic field. It also provides positive evidence than a material has effectively been struck. On a schoolyard tree struck by lightning, we were able to locate the impact to within a few centimeters, to prove that it was a vertical negative current and to estimate a peak current intensity of 99 ± 7 kA. This value is 14 kA higher than the one provided by Meteorage lightning detection network and offers an independent calibration.
Mechanical coupling between the Landers and Hector Mine (California) fault systems
Authors: Cianetti Spina , Giunchi Carlo , Cocco Massimo
Published: October 2002

A 2D finite element approach is used to model the mechanical coupling between faults and the interaction between large earthquakes. The regional tectonic stress, the fault geometry and the Coulomb friction law control the resulting slip patterns. To test the potential of this approach we investigate the Landers and Hector Mine earthquakes which occurred in southern California. The resulting coseismic displacement satisfactorily fits the available GPS data. We show that the stress changes induced by the 1992 MW = 7.3 Landers earthquake modulate the applied regional tectonic stress reducing the slip on the faults of the subsequent 1999 MW = 7.1 Hector Mine rupture. We emphasize that fault interaction due to stress transfer can alter the slip distribution of impending earthquakes.
Solitary potentials in cometary dusty plasmas
Authors: Mamun A. A. , Shukla P. K.
Published: October 2002

Recent observations reveal that plasmas in cometary tails contain charged dust grains of positive and negative polarities. Our objective here is to show that such a two‐component dusty plasma supports dust‐Langmuir and dust‐acoustic waves. The latter in the nonlinear regime propagate in the form of localized negative potentials. The role of large amplitude potential structures for trapping the positive dust grains and for the formation of dust layers of opposite polarity is discussed.
Statistics of Brazil Current rings observed from AVHRR: 1993 to 1998
Authors: Lentini Carlos A. D. , Olson Donald B. , Podestá Guillermo P.
Published: October 2002

A 6‐year time series of sea surface temperature fields derived from NOAA polar‐orbiter AVHRR 5‐day composites is used to estimate the lifetime, size, and trajectory of 43 warm‐core rings shed by the Brazil Current at the Southwestern Atlantic region in a consistent fashion for the first time. Ring lifetimes range from 11 to 95 days, and are not bi‐modal as is the case for the Gulf Stream anticyclones. Translational speeds range from 4.2 to 27.2 km/day with a mean value of 13.1 km/day. After formation, rings are mostly elliptical with a mean major radius of 126 ± 50 km and a minor radius of 65 ± 22 km. None of the rings seem to last more than four months in the region. An attempt to explore possible connections between ring shedding variability and the Antarctic Dipole is also addressed.
Secular trend in the near‐surface currents of the equatorial Pacific Ocean
Authors: Chepurin Gennady A. , Carton James A.
Published: October 2002

The westward zonal near‐surface currents of the equatorial Pacific Ocean appear to have strengthened during the past 20 years by 9–10 cm/s. Here we document this change in both near‐surface drifter and moored currents. Accompanying this increase in surface currents is a shallowing of the equatorial thermocline and a weakening of the zonal component of the equatorial trade winds. However, a simple model suggests that the most important factor is a reduction by 8 m of the average mixed layer depth over this period.
Measurements of stratospheric ClO over Antarctica in 1996–2000 and implications for ClO dimer chemistry
Authors: Solomon Philip , Connor Brian , Barrett James , Mooney Thomas , Lee Adrian , Parrish Alan
Published: October 2002

Measurements of ClO over Antarctica during the 1996 to 2000 ozone holes are compared with predictions of the SLIMCAT model. The model captures all of the major features of the measurements, including the rapid rise in August, the drop in mid or late September due to the arrival of warmer, ClOx poor air overhead, and the deactivation of ClOx into the reservoir species, HCl and ClONO2 in the ozone poor air. The model uses the standard JPL rates for the photolysis of the ClO dimer (j) and for the forward reaction forming the dimer (kf). The predicted ClO mixing ratios and columns are in excellent agreement with the measurements. A comparison of the model and data for all 5 years leads to a value of the ratio (j/kf) consistent with the standard value, namely 1.06 ± 0.30(j/kf)JPL.
Finite fault inversion of the September 25, 1999 (Mw = 6.4) Taiwan earthquake: Implications for GPS displacements of Chi‐Chi, Taiwan earthquake sequence
Authors: Chi Wu‐Cheng , Dreger Douglas
Published: October 2002

The September 25, 1999 Chi‐Chi Taiwan aftershock (Mw = 6.4) occurred on a down dip extension of the fault ruptured in the mainshock. Strong motion data were used to invert for the finite‐source process and test for the causative fault plane. We performed a grid‐search over a range of focal mechanisms and found a preferred model (strike = 5°, dip = 30°, slip = 100°) different from teleseismic studies (strike = 28±10°, dip = 27±5°, slip = 106±9°) but similar to the mainshock (strike = 5°, dip = 34°, slip = 65°). The aftershock asperity has a dimension of 10 km × 10 km with a maximum slip of ∼1.8 m and a static stress drop of 8 MPa. We forward‐predict the GPS displacements and found up to 0.033 m of surface horizontal displacements at some GPS sites, indicating that studies of post‐seismic deformation may need to account for the effects of large aftershocks.
On the reliability of Mesozoic Dipole Low: New absolute paleointensity results from Paraná Flood Basalts (Brazil)
Authors: Goguitchaichvili Avto , Alva‐Valdivia Luis M. , Urrutia Jaime , Morales Juan , Ferreira Lopes Omar
Published: October 2002

Thellier paleointensity experiments were carried out on Early Cretaceous Paraná Flood Basalts. Forty‐two samples from 11 lava flows yielded apparently reliable absolute intensity determinations. The mean paleointensity values per flow obtained in this study are ranging from 19.4 ± 4.0 to 46.7 ± 7.0 μT and the corresponding Virtual Dipole Moments are ranging from 4.0 ± 0.6 to 10.5 ± 1.1 (1022 Am2). These yield a mean value of 7.2 ± 2.3 × 1022 Am2, which is about 92% of the present geomagnetic axial dipole. Our results in conjunction with Tarduno et al.'s [2001] data suggest that the paleostrength during early Cretaceous period might be comparable or even much higher than recent field intensity and not ‘anomalousely low’ as previously suggested. Thus, the Mesozoic Dipole Low (MDL) may probably be considered as unreliable.
Wintertime mesopause temperatures observed by lidar measurements over Syowa station (69°S, 39°E), Antarctica
Authors: Kawahara T. D. , Kitahara T. , Kobayashi F. , Saito Y. , Nomura A. , She C.‐Y. , Krueger David A. , Tsutsumi M.
Published: October 2002

A sodium lidar at Syowa station (69°S, 39°E), Antarctica, measured temperature profiles from 80 to 110 km between March and September during 2000 and 2001. Monthly averaged temperature profiles in the mesopause region in wintertime (June, July and August) are nearly 20 K lower than those in the northern hemisphere sites. The measured winter mesopause altitudes (∼99 km) are in good agreement with those measured at Fort Collins (41°N) and Andøya (69°N) in winter. The mesopause temperatures (∼175 K) in winter months however are about 20 K lower than those observed from a northern hemisphere conjugate site, Andøya. The lower winter mesopause temperatures measured at Syowa station, which are consistent with southern hemisphere mesopause temperatures measured by a shipborne lidar, suggest the existence of a hemispheric difference. Possible causes for this difference are discussed.
A surface‐towed vector magnetometer
Authors: Gee J. S. , Cande S. C.
Published: October 2002

We have tested the feasibility of using a commercial motion sensor as a vector magnetometer that can be towed at normal survey speeds behind a research vessel. In contrast to previous studies using a shipboard mounted vector magnetometer, the towed system is essentially unaffected by the magnetization of the towing vessel. Results from a test deployment compare favorably with an earlier vector aeromagnetic survey, indicating that the towed instrument can resolve horizontal and vertical anomalies with amplitudes >30–50 nT. This instrument should be particularly useful in equatorial regions, where the vector anomalies are substantially greater than the corresponding total field anomalies.
Saltation Sandblasting behavior during mineral dust aerosol production
Authors: Grini Alf , Zender Charles S. , Colarco Peter R.
Published: October 2002

The dominant process in producing fine dust aerosols during saltation is thought to be sandblasting. Recent studies claim that due to competing physical processes, emission efficiencies of dust aerosols oscillate with increasing wind friction speed. These oscillations can result in order of magnitude changes in dust mass emissions. Our work shows that emission efficiencies, and hence emissions of dust aerosols are smooth functions of the wind friction speed for natural soil size distributions. This rules out oscillations as an explanation for scatter in experimental data. We show and explain the reasons for the oscillations.
The effect of nitric acid uptake on the deliquescence and efflorescence of binary ammoniated salts in the upper troposphere
Authors: Lin Jin‐Sheng , Tabazadeh Azadeh
Published: October 2002

Thermodynamic equilibrium model calculations are used to show that HNO3 can lower the relative humidity barrier to deliquesce binary ammoniated salts in the upper troposphere, particularly in aerosol solutions with an (NH4)2SO4 composition. Also in the case of (NH4)2SO4 or NH4HSO4 there is no abrupt change in the physical state of the thermodynamic system (instantaneous change of a dry salt particle into an aqueous solution) at the deliquescent point, which is typical for such a phase transition. Model results show that HNO3 dissolution in ammoniated aerosol solutions can prevent the efflorescence of (NH4)2SO4 and NH4HSO4 salts in favor of (NH4)3H(SO4)2 (letovicite) crystallization. Future laboratory experiments, where binary ammoniated salts are studied at cold temperatures in the presence of both HNO3 and H2O, are needed to confirm the results of our model calculations.
Intrinsic limits to predictability of abrupt regional climate change in IPCC SRES scenarios
Authors: Schaeffer M. , Selten F. M. , Opsteegh J. D. , Goosse H.
Published: October 2002

We used an ensemble climate‐model experiment to explore the timing and nature of an abrupt regional climate change within the 21st century. In response to global warming a North‐Atlantic climate transition occurs, which affects climate over Greenland and northwestern Europe. For a high IPCC non‐mitigation emission scenario the transition has a high probability to occur before 2100. In a lower IPCC scenario the probability is lower and the transition threshold is approached more gradually. We found that close to the threshold the evolution of the system becomes sensitive to small perturbations. Consequently, natural climate fluctuations limit the predictability of the timing of crossing the transition threshold, and thus of the abrupt climate change, most strongly for the lower IPCC scenario. No transition is projected for a mitigation scenario, in which CO2‐equivalent concentrations are stabilized below the IPCC‐scenario range.
Solitary Wave Structure in Magnetized Plasmas and the Source Region of BEN
Authors: Grabbe C. L.
Published: October 2002

A theoretical analysis of nonlinear electrostatic waves using coupled equations for a magnetized plasma yields a generalized BGK‐like equation for trapped‐particle distributions that produce these structures in the guiding‐center approximation. A conditional requirement is found for electron trapping, and the amount of trapping decreases as the angle of the electric field relative to the backgrounnd magnetic field increases, ceasing at a critical finite angle. The results are applied to broadband electrostatic waves (BEN) in the magnetail. For BEN, trapping can occur over larger angles in the near‐Earth case because of the large magnetic field there, whereas trapping is confined to close alignment with the magnetic field further out (e.g., under 20° at distances out 13 RE and above), and strongly supports the conclusion that in cases further out into the magnetotail that solitary waves are highly field‐aligned.
An ocean resonance in the Indian sector of the Southern Ocean
Authors: Webb David J. , de Cuevas Beverly A.
Published: October 2002

Satellite altimeter observations of sea surface height show an extensive region of long wavelength fluctuations in the Indian sector of the Southern Ocean. A previous study showed that a similar feature found in the South Pacific is due to a trapped geostrophic mode of the ocean. Here we investigate the feature in the Indian sector and find that it is due to a similar mode with a decay time of approximately 3.5 days. These previously unsuspected large scale modes of the ocean will have a significant effect locally on the satellite based gravity measurements currently underway.
Prodigious ash deposits near the summit of Arsia Mons volcano, Mars
Authors: Mouginis‐Mark Peter J.
Published: October 2002

Mars Orbiter Camera images are used to identify widespread material interpreted to have formed via explosive volcanism on Arsia Mons volcano, Mars. This material crops out in cliff sections associated with pit craters in layers ∼45–50 m thick. The large range of elevations where the material is found (6.2–17.5 km) suggests locally‐derived materials, although extensive reworking has produced a wide variety of dune forms. Two possible styles of volcanism appear possible for generating this material: (1) explosive volcanism associated with pit crater formation due to the release of magmatic gases, or (2) the interaction between dikes and volatile‐rich substrates. Although the best examples occur on Arsia Mons, pit craters on Ascraeus Mons also suggest explosive activity. The absence of comparable features on Olympus Mons indicates that the eruptive histories of the larger Tharsis shields were more diverse than has been inferred from Viking Orbiter images.
Earthquake potential in and around China: Estimated from past earthquakes
Authors: Rong Yufang , Jackson David D.
Published: October 2002

We present an earthquake potential estimate for magnitude 5.4 or larger earthquakes for China. The potential is expressed as the rate density, or the probability per unit area, magnitude and time, and it is based on smoothed seismicity. We constructed a special earthquake catalog, which combines previous catalogs covering different times. After deriving regression relationships, we estimated moment magnitudes for some events. Then we used the special catalog for constructing our smoothed seismicity model and testing it retrospectively. Using maximum likelihood we estimated the completeness threshold, the b‐value, and the corner magnitude. We adopted a kind of Gutenberg‐Richter distribution with modifications at higher magnitude and assumed a uniform b‐value and upper magnitude limit derived from the special catalog. From smoothed seismicity, we estimated local “a‐values”. We have begun a “prospective” test, finding that earthquakes since the beginning of 2000 are quite compatible with the model.
Parallel fault strands at 9‐km depth resolved on the Imperial Fault, Southern California
Authors: Shearer Peter M.
Published: October 2002

Precision relocation of hundreds of small earthquakes occurring along the Imperial Fault in Southern California during the last two decades reveals parallel steaks of seismicity at 9‐km depth. These strands are spaced about 0.5 km apart within a 2 km wide zone of earthquakes near the brittle‐ductile transition between the shallow locked part of the fault and a creeping zone at depth. These results suggest that the lower crustal shear zone below the Imperial Fault, site of major earthquakes in 1940 and 1979, must be at least two kilometers wide.
Impact of molecular diffusion on the CO2 distribution and the temperature in the mesosphere
Authors: Chabrillat Simon , Kockarts Gaston , Fonteyn Dominique , Brasseur Guy
Published: October 2002

Modelling the energy budget in the mesosphere and lower thermosphere requires a precise evaluation of CO2 distribution in this region. This distribution is primarily determined by competition between vertical eddy diffusion and molecular diffusion. A simple algorithm is proposed to take into account both processes, at all altitudes. Using the SOCRATES bi‐dimensional model of the middle atmosphere, we show that molecular diffusion has a direct impact on CO2 vertical distribution down to approximately 80 km altitude, i.e. well into the mesosphere and below the turbopause altitude. A sensitivity study with regard to different aeronomical processes shows that molecular diffusion has the deepest influence in the mesospheric polar night region. Our model shows that molecular diffusion of CO2 is responsible for a polar night mesopause 12 K warmer than if this process was neglected. Hence, dynamical models should take this process in account across the whole mesospheric altitude range.
Rapid ocean signals in polar motion and length of day
Authors: Ponte Rui M. , Ali Ahmed H.
Published: October 2002

Non‐tidal variability in ocean currents and bottom pressure is substantial at short periods, but relating the associated signals in ocean angular momentum (OAM) to observed polar motion and length of day fluctuations has been difficult. Our simulations using a barotropic ocean model reveal a clear connection between the estimated OAM signals and both polar motion and length of day at periods of 3–10 days. The dynamic response of the oceans to barometric pressure plays an important role in the excitation of rapid rotation signals. The impact of OAM variability is most clear when using GPS‐based Earth orientation measurements with little temporal smoothing. Using the GPS series, and accounting for OAM in addition to atmospheric effects, yields substantial improvements in the excitation budget for rapid polar motion and length of day. The comparisons with Earth rotation data provide a useful check on the rapid ocean variability simulated by the barotropic model.
Latitudinal gradients of solar wind speed around the ecliptic: Systematic displacement of the streamer belt
Authors: Mursula K. , Hiltula T. , Zieger B.
Published: October 2002

We study the effective latitudinal gradients of the solar wind (SW) speed in the two magnetic hemispheres around the heliographic equator by comparing observations at the Earth's orbit in Spring and Fall since 1964. We find that there is a large, statistically significant effective gradient of about 10 km/s/deg in the southern magnetic hemisphere around each solar minimum. However, no statistically significant effective gradient is found in the northern magnetic hemisphere. This difference implies a systematic displacement of the minimum speed locus of the streamer belt toward the northern magnetic hemisphere. We note that at least during one minimum the streamer belt and the heliospheric current sheet seem to have been oppositely displaced. We also show that the average SW speeds from the two magnetic hemispheres are roughly equal. Therefore, the earlier reported annual variation in SW speed at 1 AU is due to the displacement of the streamer belt and not due to different speeds from coronal holes of opposite polarity. The displacement of the streamer belt implies a new, persistent north‐south asymmetry related to the solar magnetic cycle which needs to be explained by realistic solar dynamo models.
Large‐amplitude internal wave generation in the lee of step‐shaped topography
Authors: Sutherland B. R.
Published: October 2002

Laboratory experiments show that as uniformly stratified fluid flows over a smoothly‐varying step, two wave‐like phenomena result: boundary‐trapped lee waves, characterized by an undular shear layer downstream of the base of the step, and internal waves, which propagate vertically away from the step. The frequency of both types of waves is an approximately constant fraction of the buoyancy frequency. The frequency of internal waves is moderately smaller than lee waves if the step size is small but, if the step size is large, the frequencies match more closely. Thus nonlinear dynamics act so that internal waves are generated not by topography alone but also by flow over the boundary‐trapped lee waves that act as “fluidic” hills. This new mechanism for internal wave generation may be an important factor in mixing over rough topography in the ocean.