bluuebunny/crossref_metadata_2025 huggingface dataset:
Late Quaternary neotectonic joints: Confirmation of the connection between jointing and contemporary tectonic stress
Authors: Khadkikar Aniruddha S.
Published: October 2002

Identification of neotectonic joints has been on the basis of correlating the orientations of vertical joints to the horizontal maximum compressive stress direction as determined from geophysical measurements. To date no study has explicitly linked neotectonic‐joint azimuths in late Quaternary sediments to maximum horizontal stress trajectories as determined geophysically. Late Quaternary coastal aeolianites from southeastern coastal Saurashtra, western India host neotectonic joints. The morphology of the neotectonic joints matches earlier contentions regarding their vertical orientations. The joints are planar irregular, show step overs between interacting joints and refraction while traversing across palaeosols‐aeolianite boundaries. Comparisons with geophysically determined maximum horizontal stress directions show that these neotectonic joints propagated in to the same direction as the SH of the contemporary tectonic stress field confirming the utility of neotectonic joints as inexpensive tools for measuring maximum horizontal stress. However, multiple joint sets suggest that even the neotectonic stress field can be complex.
An inexpensive and stable LED Sun photometer for measuring the water vapor column over South Texas from 1990 to 2001
Authors: Mims Forrest M.
Published: October 2002

A Sun photometer that uses near‐infrared light‐emitting diodes (LEDs) as spectrally‐selective photodetectors has measured total column water vapor in South Texas since February 1990. The 12 years of solar noon observations to date are correlated with upper air soundings at Del Rio, Texas (r2 = 0.75), and highly correlated with measurements by a Microtops II filter Sun photometer (r2 = 0.94). LEDs are inexpensive and have far better long term stability than the interference filters in conventional Sun photometers. The LED Sun photometer therefore provides an inexpensive, stable and portable means for measuring column water vapor.
Preindustrial atmospheric carbonyl sulfide (OCS) from an Antarctic ice core
Authors: Aydin Murat , De Bruyn Warren J. , Saltzman Eric S.
Published: October 2002

The concentration of carbonyl sulfide (OCS) has been determined in several preindustrial air samples extracted from a shallow ice core from Siple Dome, West Antarctica. The extraction of the air was carried out by shredding the core under vacuum, followed by analysis by gas chromatography with mass spectrometric detection. 11 ice core samples were analyzed, ranging in depth from 82.3 to 90.7 m. The ages assigned to OCS in the ice core samples range from 1616 to 1694 AD. The observed OCS mixing ratios range from 322.6 pptv to 442.3 pptv with a mean of 372.8 ± 37.2 pptv. These levels are significantly lower than the present day atmospheric mixing ratio of 500 pptv and suggest that the anthropogenic sources comprise approximately 25% of the present day OCS budget.
Dynamic compression of SiO2: A new interpretation
Authors: Akins Joseph A. , Ahrens Thomas J.
Published: October 2002

In light of recent discoveries of post‐stishovite phases of SiO2, with the CaCl2 and α‐PbO2 structures, we have reassigned the regimes along the Hugoniots for initial quartz, coesite, cristobalite, porous coesite, and fused silica. Calculated Hugoniots for fused silica, cristobalite and porous coesite indicate transition to stishovite, and then melt. Hugoniots for crystal quartz and coesite indicate that transition occurs to stishovite, then the CaCl2 structure and finally to melt.
Atmospheric reactive chlorine and bromine at the Great Salt Lake, Utah
Authors: Stutz Jochen , Ackermann Ralf , Fast Jerome D. , Barrie Leonard
Published: October 2002

The presence of chlorine radical species in the lower troposphere has been postulated, but only indirect evidence of its existence has been reported. We present the first direct spectroscopic observations of up to 15 ± 2 pmoles/mole‐air chlorine oxide (ClO) in the mid‐latitude boundary layer and confirm a previous discovery of the existence of bromine oxide (up to 6 ± 0.4 pmoles/mole‐air BrO). Our observations from October 2000 suggest that reactive halogens are mobilized from salt on the flats around the Great Salt Lake, Utah. The results imply levels of 105 Cl atoms per cm3, which doubles the atmospheric oxidation capacity. Ozone concentrations are anti‐correlated with the halogen oxide levels, particularly BrO, indicating that ozone depletion by catalytic reaction cycles may have occurred. If the mobilization of halogens from salt flats that was observed here is widespread, there are important implications for atmospheric chemistry and the biogeochemical cycling of mercury.
Sensitivity of the thermohaline circulation to increased CO2 and lowered topography
Authors: Vavrus Steve , Kutzbach John E.
Published: October 2002

We use an asynchronously coupled atmosphere‐ocean model to examine the response of the oceanic thermohaline circulation (THC) to increased atmospheric CO2 and lowered topography. In Experiment “3CO2”, CO2 was tripled relative to modern with no accompanying reductions in topography. In Experiment “LT3CO2”, CO2 was also tripled, in combination with lowered topography (“LT”), with elevation reductions for all major mountain ranges and ice sheets to approximate paleoclimatic conditions prior to recent major uplift and CO2 draw down (before 10 Ma). Although the THC changes from the control simulation by at least 25% in both experiments, the THC weakens with higher CO2 alone but strengthens with higher CO2 and lowered topography. The stronger THC in LT3CO2 is caused by the removal of the Tibetan Plateau and the Greenland Ice Sheet. Lowering these features alters the atmospheric circulation to promote Arctic air flow over the convective North Atlantic, thereby destabilizing the upper ocean.
Experiments on deaerating granular flows and implications for pyroclastic flow mobility
Authors: Roche O. , Gilbertson M. , Phillips J. C. , Sparks R. S. J.
Published: October 2002

Granular flows were generated by the release of beds of particles in various fluidized states, which then deaerated in a horizontal channel. We describe characteristics of the flows and their deposits. Morphological similarities between deposits in experiments and in the field suggest that pyroclastic flow deposits form from a fluidized mixture. The experiments show that slightly expanded, fluidized flows are more mobile than non‐fluidized flows of equivalent volume and material composition. They travel to a fixed distance from their source, which depends only weakly on their initial degree of fluidization. Flows of fine particles (<100 μm) deaerate slowly and are highly mobile. Pyroclastic flows commonly have large amounts of fine ash, which may have a controlling influence on their high mobility.
Retrieval of ozone column from global irradiance measurements and comparison with TOMS data. A year of data in the Alps
Authors: Masserot D. , Lenoble J. , Brogniez C. , Houet M. , Krotkov N. , McPeters R.
Published: October 2002

Spectral UV global irradiance has been measured regularly during the year 2000, in the French Alps, using two UV spectroradiometers. The total ozone column amount is retrieved from the ratio of irradiances around 305 and 340 nm, using look up tables based on modeling data. During cloudless days, ozone values from direct sun observations agree to within 5 DU. These ground based values compare reasonably well (to within about 4%, or 12 DU) with TOMS ozone data; this is consistent with the uncertainty of both methods which is estimated to 5 DU for TOMS, and 5–7 DU for clear sky ground based measurements. Generally the ground based ozone values seem to be slightly higher than the TOMS ozone values. For a few cases, the difference between TOMS and ground based values, can reach 10 to 15%. Different possible explanations of the discrepancies are considered.
In situ measurements of mesospheric turbulence during spring transition of the Arctic mesosphere
Authors: Müllemann Arno , Rapp Markus , Lübken Franz‐Josef , Hoffmann Peter
Published: October 2002

The first in situ measurements of turbulence in the upper Arctic mesosphere during the transition period from winter to summer were performed during the MIDAS/SPRING campaign in May 2000 from the Andóya Rocket Range in northern Norway (69°N). The ionization gauge CONE on board two sounding rockets identified height ranges with turbulent neutral density fluctuations which were used to determine turbulent energy dissipation rates. Accompanying in situ temperature measurements with falling spheres and remote wind measurements with a MF radar revealed the rapid seasonal change of the mesosphere's thermal structure and large scale dynamics just during the campaign. Our in situ measurements give evidence of an equally rapid change of the turbulent structure of the mesosphere within only ∼10 days. Models that take into account upward propagating gravity waves which break in the mesosphere show reasonable agreement with our findings.
Remote sensing of three‐dimensional inhomogeneous cirrus clouds using satellite and mm‐wave cloud radar data
Authors: Liou K. N. , Ou S. C. , Takano Y. , Roskovensky J. , Mace G. G. , Sassen K. , Poellot M.
Published: October 2002

We have innovated a remote sensing methodology involving the retrieval of three‐dimensional ice water content and ice crystal mean size of cirrus clouds based on a unification of satellite and ground‐based cloud profiling radar observations. This methodology has been applied to AVHRR/NOAA satellite data and mm‐wave cloud radar data obtained from the DOE's ARM program in northern Oklahoma. The three‐dimensional cloud parameter fields thus constructed are assessed with ice crystal size distributions independently derived from measurements by optical probes on board the University of North Dakota Citation. The retrieved three‐dimensional ice water contents and mean effective ice crystal sizes involving an impressive cirrus cloud occurring on April 18, 1997, are shown to be comparable to those derived from the analysis of collocated and coincident in situ aircraft measurements.
Sun/dust correlations and volcanic interference
Authors: Donarummo J. , Ram M. , Stolz M. R.
Published: October 2002

We examine the relationship between the GISP2 dust profile, a proxy for the Northern Hemisphere atmospheric dust load, and the Wolf sunspot number, a proxy for solar activity. The two records are positively correlated, but the phase of the relationship is disturbed by the effects of explosive volcanism. Similar correlation failures have already been noted for many other climatic indicators. Our work suggests that a large fraction of the correlation failures may be attributed to explosive volcanic activity.
Rainfall‐induced volcanic activity on Montserrat
Authors: Matthews Adrian J. , Barclay Jenni , Carn Simon , Thompson Glenn , Alexander Jan , Herd Richard , Williams Carlisle
Published: October 2002

Dome‐forming volcanic eruptions cyclically extrude bodies of lava over several months, which then become gravitationally unstable and collapse, generating pyroclastic flows. On 29 July 2001 extreme rainfall over Montserrat coincided with a major collapse of the Soufrière Hills lava dome. We present rainfall and seismic records that demonstrate, for the first time, a relationship between intense rainfall and lava dome collapse, with associated pyroclastic flow generation. After seven months of little rain and a period of sustained dome growth, the onset of intense rain was followed within hours by dome collapse and pyroclastic flows. The large‐scale weather system responsible for the rain was identifiable in satellite images and predicted by meteorological forecasts issued 60 hours prior to the volcanic activity. It is suggested that weather prediction of intense rainfall be incorporated with existing geophysical and geochemical measurements to improve warnings of these hazardous events.
Climate sensitivity and thermal inertia
Authors: Wu Qigang , North Gerald R.
Published: October 2002

We compare several Atmosphere/Ocean General Circulation model control runs by fitting long control runs to a simple discrete (annual averages) stochastic model: Rate of change of global heat content = difference of absorbed and emitted radiation + white noise. If the heat content is taken to be proportional to the surface temperature we can estimate the effective (broad frequency‐band averaged) heat capacity for the system by a regression procedure. We find a wide range of effective heat capacities that correlate significantly with the published sensitivities of the models. Models with large sensitivities have large thermal inertia. Several interpretations are discussed.
Traveling waves in the Northern Hemisphere of Mars
Authors: Wilson R. John , Banfield Don , Conrath Barney J. , Smith Michael D.
Published: October 2002

Analysis of temperature retrievals from Mars Global Surveyor Thermal Emission Spectrometer data has revealed the presence of regular, eastward propagating waves in the Northern Hemisphere. A large amplitude, zonal wave 1 with a long (∼20 sol) period is particularly prominent during early winter (Ls = 220–270°). After Ls = 270°, a weaker and more rapidly propagating (6.5 sol period) zonal wave 1 is dominant. These waves have a deep vertical structure (>40 km) correlated with the axis of the winter hemisphere westerly jet. Simulations with a Mars general circulation model suggest that the fast wave is associated with baroclinic instability due to the strong meridional temperature gradient at the surface and is consistent with surface pressure oscillations seen in Viking Lander data. By contrast, the slow wave has the appearance of a large‐amplitude Rossby wave that is coupled with an inertially unstable region in the subtropics.
Twentieth century secular decrease in the atmospheric potential gradient
Authors: Harrison Giles
Published: October 2002

Current flowing in the global atmospheric electrical circuit (AEC) substantially decreased during the twentieth century. Fair‐weather potential gradient (PG) observations in Scotland and Shetland show a previously unreported annual decline from 1920 to 1980, when the measurements ceased. A 25% reduction in PG occurred in Scotland 1920–50, with the maximum decline during the winter months. This is quantitatively explained by a decrease in cosmic rays (CR) increasing the thunderstorm‐electrosphere coupling resistance, reducing the ionospheric potential VI. Independent measurements of VI also suggest a reduction of 27% from 1920–50. The secular decrease will influence fair weather atmospheric electrical parameters, including ion concentrations and aerosol electrification. Between 1920–50, the PG showed a negative correlation with global temperature, despite the positive correlation found recently between surface temperature and VI. The 1980s stabilisation in VI may arise from compensation of the continuing CR‐induced decline by increases in global temperature and convective electrification.
Core flooding laboratory experiment validates numerical simulation of induced permeability change in reservoir sandstone
Authors: Bartels Jörn , Kühn Michael , Schneider Wilfried , Clauser Christoph , Pape Hansgeorg , Meyn Volker , Lajcsak Ivo
Published: October 2002

Numerical simulation of reactive transport was validated in a core flooding experiment simulating conditions in a managed geothermal reservoir. Permeability was measured along a sandstone core prepared with anhydrite and subjected to a temperature gradient. Anhydrite was dissolved and precipitated in the cold upstream and hot downstream regions of the core, respectively. The numerical code SHEMAT was used to simulate coupled transport and chemical reactions at the temperature front (http://www.rwth-aachen.de/geop/shemat/). It comprises an extended version of the geochemical speciation code PHRQPITZ for calculating chemical reactions in brines of low‐high ionic strength and temperatures of 0–150°C. Permeability is updated to porosity via a novel, calibrated power‐law based on a fractal pore‐space model resulting in a large exponent of 11.3. Simulation results agree well with measured permeability. This both validates the model and demonstrates that the fractal relationship is crucial for a successful simulation of this type of reactive transport.
Importance of shapes and compositions of wind‐blown dust particles for remote sensing at solar wavelengths
Authors: Kalashnikova Olga V. , Sokolik Irina N.
Published: October 2002

The quality of satellite aerosol retrievals depends critically upon the modeling accuracy of the aerosol optical properties. The optical properties of mineral aerosols depend on particle morphology, mineralogy, and state of mixing. Here we investigate how the realistic morphology and composition of dust particles affect the optical properties of dust mixtures by utilizing microscopy data that recently become available of dust samples collected in the atmosphere. The data were used to reconstruct the representative composition‐shape‐size (CSS) distributions and then the discrete dipole approximation technique was applied to calculate the optical properties. We demonstrate that the presence of sharp‐edge, angular‐type particles results in various differences in the scattering phase function, asymmetry parameter, optical depth and single scattering albedo compared to those of the volume‐equivalent spheres or ellipses. These differences are sufficiently large as to affect the retrievals of aerosol optical properties from satellite and ground‐based remote sensing observations at the solar wavelengths.
Ocean Raman scattering in satellite backscatter UV measurements
Authors: Vasilkov Alexander P. , Joiner Joanna , Gleason James , Bhartia Pawan K.
Published: October 2002

Vibrational Raman scattering by liquid water (ocean Raman scattering) significantly contributes to the filling‐in of solar Fraunhofer lines observed by satellite backscatter ultraviolet (buv) instruments in the cloudless atmosphere over clear ocean waters. A radiative transfer model accounting for this effect in buv measurements has been developed and the results compared with observations from the European Space Agency's Global Ozone Monitoring Experiment (GOME). The model extends existing models for ocean Raman scattering to the UV spectral range. Ocean Raman scattering radiance is propagated through the atmosphere using a concept of the Lambert equivalent reflectivity and an accurate radiative transfer model for Rayleigh scattering. The good agreement between model and observations suggests that buv instruments may be useful for estimating chlorophyll and dissolved organic matter contents.
Power‐law velocity distributions in fracture networks: Numerical evidence and implications for tracer transport
Authors: Painter Scott , Cvetkovic Vladimir , Selroos Jan‐Olof
Published: October 2002

Velocity distributions in two‐ and three‐dimensional networks of discrete fractures are studied through numerical simulations. The distribution of 1/v, where v is the velocity along particle trajectories, is closely approximated by a power law (Pareto) distribution over a wide range of velocities. For the conditions studied, the power law exponents are in the range 1.1–1.8, and generally increase with increasing fracture density. The same is true for the quantity 1/bv, which is related to retention properties of the rock; b is the fracture half‐aperture. Using a stochastic Lagrangian methodology and statistical limit theorems applicable to power‐law variables, it is shown that the distributions of residence times for conservative and reacting tracers are related to one‐sided stable distributions. These results are incompatible with the classical advection dispersion equation and underscore the need for alternative modeling approaches.
Rapid afterslip following the 1999 Chi‐Chi, Taiwan Earthquake
Authors: Hsu Ya‐Ju , Bechor Noa , Segall Paul , Yu Shui‐Beih , Kuo Long‐Chen , Ma Kuo‐Fong
Published: October 2002

Postseismic displacements of as much as 14 cm were recorded by GPS measurements in the 3 months following the MW 7.6 1999 Chi‐Chi, Taiwan earthquake. Data from 35 continuous and 90 campaign‐surveyed stations, which show continued east over west thrusting, are analyzed to estimate the postseismic slip distribution and fault geometry. Assuming the shallow fault dips 24° E, as determined by numerous studies of the mainshock, we invert for the deeper fault structure. Our results show that the fault dip shallows with depth below the hypocenter, merging into a nearly horizontal decollement at a depth of 8–12 km. The afterslip distribution shows a maximum slip of 25 cm in the hypocentral region at 7–12 km depth as well as significant slip on the lower decollement. Afterslip is notably absent in the region of maximum coseismic slip, consistent with the afterslip being driven by the mainshock stress change.
Evidence for xenon silicates at high pressure and temperature
Authors: Sanloup Chrystèle , Hemley Russell J. , Mao Ho‐kwang
Published: October 2002

We present evidence for the stability of xenon silicate phases at deep crustal conditions. High pressure‐temperature investigations of the Xe‐SiO2 system were conducted using diamond‐anvil cells combined with laser heating and external resistive heating. A new compound was synthesized at 0.7–1.5 GPa and 1500–1750° as evidenced by Raman spectroscopy. Upon temperature quenching, the material undergoes a back transformation to another Xe‐SiO2 phase stable up to 2.14 GPa. X‐ray diffraction data show that this second phase has a cubic structure [a = 8.03(±0.03) Å] and a bulk modulus of 20(±0.6) GPa. The phase was found to have a minimum of 4 wt% Xe from electron microprobe analysis. These results indicate that the chemical affinity of Xe and silica increases at high pressures and temperatures. Hence Xe can be potentially hosted by silicates in the crust, which helps to resolve the geochemical paradox of the ‘missing Xe’ in the atmospheres of the Earth and Mars.
A five years super‐slow aseismic precursor model for the 1994 M8.3 Hokkaido‐Toho‐Oki lithospheric earthquake based on tide gauge data
Authors: Katsumata Kei , Kasahara Minoru , Ozawa Shinzaburo , Ivashchenko Alexei
Published: October 2002

Here we present a super‐slow aseismic event model prior to the magnitude 8.3 Kurile Island (Hokkaido‐Toho‐Oki) earthquake on 4 October 1994 based on data recorded by two tide gauges, located 50–150 km from the earthquake epicenter. Both instruments recorded several cm of subsidence during a five‐year period prior to the earthquake. The observed signals are consistent with a precursory quasi‐stable slip on the western half of the Hokkaido‐Toho‐Oki fault plane. When recognized, such aseismic events can considerably improve our intermediate‐term (several years) prediction capability.
A marine source of methyl nitrate
Authors: Moore Robert M. , Blough Neil V.
Published: October 2002

Methyl nitrate (CH3ONO2) is known to be an important source of reactive nitrogen in the remote marine atmosphere, and it has been speculated that its atmospheric distribution might be explained in part by an ocean source. Measurements made in the N. Atlantic show that dissolved CH3ONO2 is present at depths up to 600–800 m. Maximum concentrations are typically found in the upper water column, indicative of an in situ source. Although we show that CH3ONO2 can be produced photochemically in seawater in the presence of nitrite, and that this reaction may account for some production in the uppermost waters of the ocean, the maxima below this zone indicate that an additional production mechanism exists.
Chemiion evolution in motor vehicle exhaust: Further evidence of its role in nanoparticle formation
Authors: Yu Fangqun
Published: October 2002

The evolution of engine‐generated chemiions in a vehicle tailpipe or in a sampling transfer line is studied and the key parameters controlling chemiion concentration at the exit plane are investigated. We find that the observed higher number concentration but smaller size of nuclei mode particles associated with shorter transfer line residence time, enhanced nanoparticle emission associated with reduced soot emission, and increase in the number concentration but decrease in the size of nuclei mode particles associated with increasing traffic speed, can all be consistently explained by the reduced loss of ions in the transfer line or tailpipe. This provides further evidence that engine‐generated chemiions play a key role in the formation of the nanoparticles in motor vehicle exhaust.
Observation of western boundary current atmospheric convergence zones using scatterometer winds
Authors: Pan Jiayi , Yan Xiao‐Hai , Zheng Quanan , Liu W. Timothy
Published: October 2002

A merged scatterometer wind data set from ERS‐1/2, NSCAT, and QuikSCAT missions was used to observe the atmospheric convergence zones (ACZs) caused by the western boundary currents, the Gulf Stream and Kuroshio. The long‐term means of the atmospheric convergence show the ACZs' spatial features, which are related to the precipitation patterns in these regions. Seasonal images of the ACZs were produced to show annual cycles of the ACZs, indicating that the intensities of the ACZs over these two regions strengthen in winter and weaken in summer. Furthermore, we calculated the total convergence over the Gulf Stream and Kuroshio ACZs, which is defined as the integral of the convergence over the ACZs. The interannual variability of the total convergence was extracted by using a multi‐stage filter, revealing that in response to strong El Niño events in 1991–92 and 1997–98, the total convergence reached maxima.
Temporal changes in dissolved oxygen of the intermediate water in the subarctic North Pacific
Authors: Andreev Andrey , Watanabe Shuichi
Published: October 2002

Using an approximately 50‐year data set, the changes in dissolved oxygen (DO) on isopycnals in the intermediate layer of the subarctic North Pacific were analyzed. The temporal variations in DO on a decadal scale in the western subarctic Pacific display a negative correlation with those in the eastern subarctic Pacific. From 1950 to 2000 there is an average increase in the Apparent Oxygen Utilization (AOU) with a rate of 0.3 ± 0.2 (95% confidence interval) μmol kg−1 y−1 in the Western Subarctic Gyre (WSG) and Alaska Gyre (AG). The increase in AOU coincides with an increased temperature in the intermediate layer‐ (0.31 ± 0.28°C century−1 in the WSG and 0.54 ± 0.32°C century−1 in the AG) and decrease in surface‐water salinity in the Bering Sea (−0.32 ± 0.22 century−1). It is hypothesized that the changes are correlated with the North Pacific Index (NPI), which fosters meridional transport of salt to the Bering Sea when it is high. The gradual decrease in NPI thus has caused a freshening and a subsequent decrease in the ventilation resulting in an AOU increase in the intermediate waters of the subarctic North Pacific.
An explanation for strongly underwound magnetic field in co‐rotating rarefaction regions and its relationship to footpoint motion on the the sun
Authors: Schwadron N. A.
Published: October 2002

Strongly underwound magnetic field is observed to be correlated with the occurrence of co‐rotating rarefaction regions (CRRs). We demonstrate that the phenomenon is likely caused by the combined action of (1) the motion of footpoints of open magnetic field lines on the Sun from within to outside coronal hole boundaries; and (2) the effect of solar wind shearing in rarefaction regions. We provide formulas that may be used to relate the observed underwinding of magnetic field lines in CRRs to infer the velocities of footpoints through coronal hole boundaries. The observations of strong field underwinding in CRRs generally confirms the hypothesis that the footpoints of open magnetic field lines move on the Sun through coronal holes, the sources of fast solar wind.
The arrival of a « new » Labrador Sea Water signal in the tropical Atlantic in 1996
Authors: Freudenthal Sébastien , Andrié Chantal
Published: October 2002

We describe results inferred from the tracking, in the tropical Atlantic, of CFC signals linked to the intensification of convection processes in the Labrador Sea since 1988. CFC and hydrology series (1993–1997) off French Guiana (7°N) have been investigated in order to analyse LSW characteristics and their variability. A dramatic increase of the CFC concentrations below 2000 m at the level of the classical LSW has been observed in April 1996. Using CFC and salinity data, the comparison of the (1993–1997) series at 7°N with a (1989–1999) series at 35°W indicates that the sporadic 1996 event has been followed in the equatorial Atlantic in the late 90s by the arrival of a more continuous newly ventilated LSW flow. This study evaluates a transit time from the Labrador basin to the tropics of less than one decade, in agreement with direct current measurements.
CO2 exchange coefficients from remotely sensed wind speed measurements: SSM/I versus QuikSCAT in 2000
Authors: Carr Mary‐Elena , Tang Wenqing , Liu W. Timothy
Published: October 2002

We compare here the air‐sea exchange coefficient for CO2 estimated with monthly mean wind speed measured by the Special Sensing Microwave Imager (SSM/I), KS, and by the scatterometer QuikSCAT, KQ, for the year 2000. KS and KQ present the same patterns, although are larger than in ∼65% of the world ocean. Zonal mean KS are consistently larger, except ∼50°S and north of 10°S in the Indian Ocean. Global oceanic uptake, FQ, estimated using KQ and climatological ΔpCO2 ranges from 0.43 (July) to 2.6 Gt C y−1 (December). The global sink estimated from SSM/I is ∼10% larger than FQ for most of the year. This comparison supports the use of SSM/I to quantify interannual variability of the global exchange coefficient of CO2.
Ensemble canonical correlation prediction of precipitation over the Sahel
Authors: Mo Kingtse C. , Thiaw Wassila M.
Published: October 2002

Ensemble canonical correlation (ECC) prediction method is applied to predict summer rainfall over the Sahel. The predictors are the global sea surface temperature (SST), 200‐hPa streamfunction with zonal means removed (PSI), and forecasts or simulations from the climate models. The canonical correlation analysis (CCA) is performed for each variable separately. These predicted precipitation fields form an ensemble. The ensemble mean is the equal weighted average of its members. For both the multi‐model simulations and seasonal hindcasts, the CCA correction improves forecast skill. The ensemble, which consists of the CCA precipitation forecasts based on SST, PSI and the CCA corrected model simulations gives the highest skill. Each member has forecast skill over the different parts of the Sahel. Therefore, the ensemble mean has higher skill than its individual members.
OH observations of space shuttle exhaust
Authors: Stevens Michael H. , Englert Christoph R. , Gumbel Jörg
Published: October 2002

We report the unexpected observation of a large hydroxyl (OH) cloud north and east of the United States a day after a space shuttle launch in November, 1994. The Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI) observed OH(0,0) solar fluorescence near 309 nm while staring toward a tangent altitude of 87 km, where OH can be produced from water vapor photodissociation. The OH(0,0) band has a rotational temperature of 252 ± 23 K corresponding to an altitude of 110 ± 3 km, where nearly half of the shuttle's main engine water vapor exhaust is released on ascent. The location of the cloud one day after injection into the atmosphere implies that its average velocity is between 26–40 m/s northward. We also report strong evidence of water ice measured simultaneously along the same line of sight, suggesting that water vapor exhaust is redistributed by condensation and sedimentation.
Photochemical production of nitrous acid on glass sample manifold surface
Authors: Zhou Xianliang , He Yi , Huang Gu , Thornberry Troy D. , Carroll Mary Anne , Bertman Steven B.
Published: October 2002

Significant production of HONO was observed on glass sample manifold wall surface when exposed to sunlight during the PROPHET 2000 summer measurement intensive. It is hypothesized that the artifact HONO was produced by photolysis of adsorbed nitric acid/nitrate on the manifold wall surfaces followed by the subsequent reaction of produced NO2 and adsorbed H2O on surface. This observation suggests against the use of an unshielded glass manifold as a sampling inlet for the measurement of atmospheric HONO. It may also have some implications in interpreting field NOx data measured using similar glass inlet manifolds, especially from the clean remote environments where NOx is low and HNO3 is a major fraction of NOy.
Coseismic hydrological changes associated with dislocation of the September 21, 1999 Chichi earthquake, Taiwan
Authors: Lee Min , Liu Tsung‐Kwei , Ma Kuo‐Fong , Chang Yen‐Ming
Published: October 2002

Being situated in the immediate vicinity of the 1999 Chichi earthquake epicenter, 178 automatic‐recording monitoring wells of the Choshui fan‐delta provided a very valuable data set for testing whether the coseismic water‐level changes in confined aquifers can be explained as a poroelastic response of well‐aquifer systems to coseismic volumetric strain. This study demonstrates that the polarities of the observed coseismic water‐level and river discharge changes are in good agreement with those of the static volumetric strain calculated by a dislocation model, using the well‐constrained rupture model of the seismogenic Chelungpu fault. The puzzling “bull‐eye” patterns formed by the equipotential lines of the coseismic water‐level changes in the confined aquifers in the middle parts of the fan‐delta represent pressure enhancement due to their being situated at the pinch‐out ends of conglomeratic layers.
Wind/SWE observations of firehose constraint on solar wind proton temperature anisotropy
Authors: Kasper Justin C. , Lazarus Alan J. , Gary S. Peter
Published: October 2002

The proton resonant firehose instability may arise in collisionless plasmas in which the proton velocity distribution is approximately bi‐Maxwellian with T∥p/T⊥p > 1, where ⊥ and ∥ denote directions relative to the background magnetic field B○. Linear theory and one‐dimensional simulations predict that enhanced field fluctuations from the proton resonant firehose instability impose a constraint on proton temperature anisotropies of the form 1 − T⊥p/T∥p = Sp/β∥pαp where β∥p ≡ 8πnpkBT∥p/B○2, and the fitting parameters Sp ∼ 1 and αp ≃ 0.7. Observations from the Wind spacecraft are reported here. These measurements show for the first time with a comprehensive plasma and magnetic field data set that this constraint is statistically satisfied in the solar wind near 1 AU, with best‐fit values of Sp = 1.21 ± 0.26 and αp = 0.76 ± 0.14.
Improving accuracy of near real‐time Precipitable Water Vapor estimation with the IGS predicted orbits
Authors: Liu Yanxiong , Chen Yongqi
Published: October 2002

The accuracy of estimated Precipitable Water Vapor (PWV) content in near real time using ground based GPS/Met strongly depends on the quality of GPS orbits. The impact of the predicted GPS orbits in IGS Ultra‐rapid products on PWV estimation is investigated in this paper. A few satellites of poor orbits will contaminate the estimated PWV. In this study, variance ratios derived from adjusted GPS double difference carrier phase observations for different satellites are used to identify poor GPS orbits. By excluding or down weighting the measurements related to those poor satellites, the accuracy of PWV estimation can be significantly improved.
Response of the equatorial ionosphere in the Indian (midnight) sector to the severe magnetic storm of July 15, 2000
Authors: Sastri J. Hanumath , Niranjan K. , Subbarao K. S. V.
Published: October 2002

During the severe magnetic storm of July 15, 2000, an impulsive and remarkably large downward movement of F region occurred simultaneously at locations throughout the equatorial region (dip 0.3–20°N) in the Indian sector, in close association with episodes of rapid ring current intensification. The abnormal midnight descent of equatorial F region (maximum amplitude close to the magnetic equator, 215 km/hr) indicative of a short‐lived westward electric field disturbance (peak amplitude ≈4.6 mV/m) is interpreted as the signature of prompt penetration electric fields associated primarily with impulsive ring current injections. The westward electric field disturbance in the Indian (midnight) sector occurred near simultaneous with the eastward electric field disturbances in the dusk sector, reported by Basu et al. [2001a]. Moreover, the prompt electric field penetration to the magnetic equator both in the dusk and midnight sectors occurred in an environment already under the influence of ionospheric disturbance dynamo (IDD) electric fields, illustrating the profound manner in which the equatorial F region plasma dynamics can get modified globally during the main phase of severe magnetic storms.
Mechanism study of the ENSO and southern high latitude climate teleconnections
Authors: Liu Jiping , Yuan Xiaojun , Rind David , Martinson Douglas G.
Published: October 2002

Evidence of El Niño‐Southern Oscillation (ENSO) teleconnections in the southern high latitude climate has been identified, although the mechanisms that might lead to such far‐reaching teleconnections remain unresolved. Here we propose one such mechanism‐the regional mean meridional atmospheric circulation (the regional Ferrel Cell)‐responsible for the covariability of the ENSO and Antarctic Dipole (ADP; a predominant interannually‐varying signal in the southern high latitudes). It is found that the altered storm tracks associated with the ENSO variability influence the regional Ferrel Cell indirectly by changing the meridional eddy heat flux divergence and convergence, and shifting the latent heat release zone. The changes of the regional Ferrel Cell then influence the southern high latitude climate by modulating the mean meridional heat flux.
The polar cap magnetic activity indices in the southern (PCS) and northern (PCN) polar caps: Consistency and discrepancy
Authors: Lukianova R. , Troshichev O. , Lu Gang
Published: October 2002

There are some systematic differences between the 1‐min Polar Cap (PC) indices of magnetic activity derived from data from the southern hemispheric station, Vostok, and the northern hemispheric station, Thule. First of all, differences in sign of the PC index are observed when BZ is northward: negative values of the PC index are common in the summer polar cap. Secondly, predominance of larger PC index values is seen in winter hemisphere for extremely high levels of magnetic activity (PC > 12) when the ionospheric electric field in summer and winter polar caps tends to approach an asymptotic value of E = 40–45 mV/m. It is suggested that ionospheric conductivity in the winter polar cap can be significantly increased owing to bombardment of the ionosphere by solar protons (E = 1–10 MeV) in association with polar cap absorption events.
Electron heat flux instabilities in coronal holes: Implications for ion heating
Authors: Markovskii S. A. , Hollweg Joseph V.
Published: October 2002

There is growing evidence that the heating of the ions in solar coronal holes and the resulting generation of the fast solar wind is due to cyclotron‐resonant damping of ion cyclotron waves. At the same time, the origin of these waves is not understood. In this paper, it is suggested that the waves in the proton cyclotron frequency range are generated by a plasma microinstability due to a heat flux coming from the Sun. A new view is used according to which heat flux is launched intermittently by small‐scale reconnection events (nanoflares) at the coronal base. This allows the heat flux to be sporadically large enough to drive the instabilities, while at the same time satisfying the time‐averaged energy requirements of the solar wind. It is shown that in a low‐beta coronal plasma an electrostatic heat‐flux instability has a comparable threshold and much greater growth rate than a shear Alfvén heat flux instability. The implications of these instabilities for the ion heating in the coronal holes are discussed.
Temporal and Spatial Features of Waves and Electron Holes Driven by Double Layers and Their Relevance to VLF Saucers
Authors: Singh Nagendra
Published: October 2002

Motivated by the observations of electron holes (EHs) strongly correlated with VLF saucers, the basic idea explored here is that when the parallel potential drop in a developing diverging electrostatic shock encounters a localized density cavity, a set of plasma processes are triggered including (i) formation of an upward‐moving double layer (DL), (ii) setting up of potential gradients in which counterstreaming of electrons occurs on the DL's high‐potential side, and (iii) generation of wave packets containing linear and nonlinear waves, such as the EHs. We specifically examine here the temporal and spatial evolution of such wave packets (WPs) in a one‐dimensional Vlasov simulation. If such evolution persists in multi‐dimensional treatments, the frequency dependent angular dispersion of the WPs could generate VLF saucers. A rapid growth of the wave packets to large amplitudes within a distance of about hundred Debye lengths gives an effective mechanism for the localization of the source for the saucers. Estimates show that the electrostatic energy stored in a wave packet containing just a few large‐amplitude EHs is sufficient to power typical VLF saucer events.
On the physical nature of the Arctic Oscillation
Authors: Christiansen Bo
Published: October 2002

Recently, it has been debated if the Arctic Oscillation (AO) is a physical oscillation or if it appears as a difference between two regimes. Indications for the latter view include the peaks found in the probability density function in the space spanned by the two leading Empirical Orthogonal Functions (EOFs) of the Northern Hemisphere wintertime 500 hPa heights, and the statistical dependence of these modes. We show that only one of the three reported peaks is statistically significant. Furthermore, an orthonormal rotation suggested by the form of the probability density function itself removes both the statistical dependence and the peaks. The rotated EOFs resemble the patterns of the Pacific/North‐American Oscillation and the AO, respectively. The rotation also simplifies the description of the connection to the stratosphere. The phase of the second rotated EOF (the AO) depends strongly on the sign of the stratospheric zonal mean zonal wind 30 days before.
Tsunami earthquakes possibly widespread manifestations of frictional conditional stability
Authors: Bilek S. L. , Lay T.
Published: October 2002

Tsunami earthquakes, shallow events that produce larger tsunamis than expected given their surface wave magnitudes (Ms), typically have long durations and a source spectrum depleted in short period energy. Seven cases of underthrusting tsunami earthquakes provide information on the rupture processes, but little constraint on geographic distribution or frequency. We compare their rupture characteristics with smaller magnitude earthquakes on circum‐Pacific interplate thrust faults. Comparable moment release time histories are found for large tsunami earthquakes and for many smaller shallow subduction zone earthquakes, with significantly longer durations and additional source complexity than for events deeper than 15 km. Thus, very shallow interplate earthquake ruptures are scale invariant, with variable frictional properties on the plate interface controlling the depth dependent rupture process. Widespread occurrence of small shallow interplate earthquakes with long durations suggests that many subduction faults have frictional properties that may enable large tsunami‐generating earthquakes to occur; fortunately, large shallow ruptures are infrequent.
Adjustment of the coupled ocean–atmosphere system to a sudden change in the Thermohaline Circulation
Authors: Dong B.‐W. , Sutton R. T.
Published: October 2002

The adjustment of the coupled ocean–atmosphere system to a fresh water anomaly in the North Atlantic Ocean is investigated using a coupled GCM. In response to the anomaly the Atlantic Thermohaline Circulation (THC) collapses, and the associated reduction in northward heat transport causes sea surface temperatures (SST) to fall over the North Atlantic, and to increase over the tropical South Atlantic. Atmospheric feedbacks are excited as soon as the SST anomalies reach sufficient magnitude. A key stage in the adjustment process occurs 4–6 years after the perturbation is introduced when a significant SST dipole develops in the tropical Atlantic. This dipole causes a southward shift of the ITCZ and leads, in year 7, to the triggering of an El Niño event. It is concluded that atmospheric feedbacks could spread globally the influence of a sudden change in the THC much more quickly and efficiently than could ocean processes alone.
Low frictional strength of quartz rocks at subseismic slip rates
Authors: Goldsby David L. , Tullis Terry E.
Published: October 2002

Laboratory experiments on rocks at low sliding velocity typically yield values of the friction coefficient of 0.6–0.85. Here we demonstrate that an extraordinary decrease in friction coefficient accompanies sliding of ‘room dry’ quartz rocks at rates faster than in most laboratory experiments, but slower than seismic slip rates. In some cases, the friction coefficient decreases from low‐speed values by more than a factor of 3. This extraordinary weakening likely results from the formation of finely comminuted, amorphous, wet material on the sliding surface.
On the use of sedimentation rates in deciphering global change
Authors: Métivier François
Published: October 2002

The amount of sediment deposited through time at a given place is controlled by both tectonic and climatic factors that change over several length and time scales. For these reasons the sedimentary record is commonly exploited to study global change. To understand this record, most studies have relied on assembling data from a few localities within a given reservoir and have extrapolated those data to whole of the reservoir. Here it is shown not only that this approach has very large inherent uncertainties, but also that the use of extrapolating sedimentary records has little physical significance. A much better approach, although much more difficult, is via a full, three‐dimensional mass balance calculation.
The temperature structure of the winter atmosphere at South Pole
Authors: Pan Weilin , Gardner Chester S. , Roble Raymond G.
Published: October 2002

Fe/Rayleigh lidar measurements and balloon observations made recently at the geographic South Pole are used to characterize the monthly mean winter temperature profiles from the surface to about 110 km. The measured temperatures during mid‐winter in both the stratopause and mesopause regions are 20–30 K colder than current model predictions. These differences are caused by weaker than expected compressional heating associated with subsidence over the polar cap. The measured mesopause temperature responds much more rapidly to changes in sunlight than model predictions, which suggests that IR heating by CO2 absorption may also be important to the thermal balance in the mesopause region.
Can chemical effects on cloud droplet number rival the first indirect effect?
Authors: Nenes Athanasios , Charlson Robert J. , Facchini M. Cristina , Kulmala Markku , Laaksonen Ari , Seinfeld John H.
Published: October 2002

An increase in cloud droplet number concentration resulting from an increase in ambient aerosol (and subsequent albedo increase) is typically identified as the first indirect (or “Twomey”) climatic effect of aerosols [Twomey, 1974]. A key question is whether chemical effects (dissolution of soluble gases and slightly soluble substances, surface tension depression by organic substances and accommodation coefficient changes) could potentially rival changes in droplet number from changes in aerosol number concentration. We assess the sensitivity of cloud droplet number concentration to such chemical factors, using a cloud parcel model. We find that numerous conditions exist, for which chemical influences on cloud droplet activation can indeed rival the Twomey effect.