bluuebunny/crossref_metadata_2025 huggingface dataset:
Satellite observation of dehydration in the Arctic Polar stratosphere
Authors: Pan L. L. , Randel W. J. , Nakajima H. , Massie S. T. , Kanzawa H. , Sasano Y. , Yokota T. , Sugita T. , Hayashida S. , Oshchepkov S.
Published: October 2002

We report the first space‐borne observation of dehydration in the Arctic polar stratosphere. In January 1997, the Improved Limb Atmospheric Spectrometer (ILAS) observed up to ∼3 ppmv water vapor reduction during ice cloud formation and ∼2 ppmv permanent removal of water vapor, mostly at altitudes between 23 and 26 km. In some cases, the dehydrated air was downwind from mountain wave induced Polar Stratospheric Cloud (PSC) events. Furthermore, simultaneous observations of HNO3 and H2O show that the gas phase reduction of HNO3 in the Arctic (January 1997) was much smaller than that observed in the Antarctic (June 1997) when a similar level of water vapor reduction occurred.
On the midlatitude thermal response to tropical warmth
Authors: Robinson Walter A.
Published: October 2002

Observations reveal a global‐scale thermal response to El Niño and La Niña, featuring a band of tropospheric anomalies opposite in sign to those in the tropics. When an idealized dynamical model is forced by increased tropical heating, a similar response, with an enhanced subtropical thermal gradient, results. In the idealized model, this response is produced by changes in transient eddy fluxes of heat and momentum, and consequent changes in the mean meridional circulation. The similarity between the two‐level model results and those from observations, as well as the zonally averaged behavior of a GCM, suggests that the same dynamics operate in nature. This represents a tropical‐midlatitude teleconnection distinct from and in addition to that mediated by stationary Rossby wave trains.
Cloud variability as revealed in outgoing infrared spectra: Comparing model to observation with spectral EOF analysis
Authors: Huang Xianglei , Farrara John , Leroy Stephen S. , Yung Yuk L. , Goody Richard M.
Published: October 2002

Spectrally resolved outgoing radiance is a potentially powerful tool for testing climate models. To show how it can be used to evaluate the simulation of cloud variability, which is the principal uncertainty in current climate models, we apply spectral empirical orthogonal function (EOF) analysis to satellite radiance spectra and synthetic spectra derived from a general circulation model (GCM). We show that proper averaging over a correct timescale is necessary before applying spectral EOF analysis. This study focuses on the Central Pacific and the western Pacific Warm Pool. For both observation and GCM output, cloud variability is the dominant contributor to the first principal component that accounts for more than 95% of the total variance. However, the amplitude of the first principal component derived from the observations (2 ∼ 3.4 W m−2) is 2 ∼ 6 times greater than that of the GCM simulation. This suggests that cloud variability in the GCM is significantly smaller than that in the real atmosphere.
Advection from the North Atlantic as the forcing of winter greenhouse effect over Europe
Authors: Otterman J. , Angell J. , Atlas R. , Bungato D. , Schubert S. , Starr D. , Susskind J. , Wu M.‐L. C.
Published: October 2002

In winter, large interannual fluctuations in the surface temperature are observed over central Europe. Comparing warm February 1990 with cold February 1996, a satellite‐retrieved surface (skin) temperature difference of 9.8 K is observed for the region 50–60°N; 5–35°E. Previous studies show that advection from the North Atlantic constitutes the forcing to such fluctuations. The advection is quantified by Index Ina, the average of the ocean‐surface wind speed over the eastern North Atlantic when the direction is from the southwest (when the wind is from another direction, it counts as a zero speed to the average). Average Ina for February 1990 was 10.6 m s−1, but for February 1996 Ina was only 2.4 m s−1. A large value of Ina means a strong southwesterly flow which brings warm and moist air into central Europe at low level, producing a steeper tropospheric lapse rate. Strong ascending motions at 700 mb were observed in association with warm and moist advection from the ocean in February 1990, producing clouds and precipitation. Total precipitable water and cloud‐cover fraction have larger values in February 1990 than in 1996. The difference in the greenhouse effect between these two scenarios, this reduction in the heat loss to space, can be translated into a virtual radiative heating of 2.6 W m−2 above the February 1990 surface/atmosphere system, which contributes to a warming of the surface on the order of 2.6 K. Accepting this estimate as quantitatively meaningful, we evaluate the direct effect, the rise in the surface temperature in Europe as a result of the maritime‐air inflow, as 7.2 K (9.8 K–2.6 K). Thus, fractional reinforcement by the greenhouse effect is 2.6/7.2, or 36%, a substantial positive feedback.
Equation of state of the hydrous phase δ‐AlOOH at room temperature up to 22.5 GPa
Authors: Vanpeteghem Carine B. , Ohtani Eiji , Kondo Tadashi
Published: October 2002

The equation of state of δAlOOH has been determined at room temperature up to 22.5 GPa by angle‐dispersive x‐ray diffraction using synchrotron radiation. The isothermal bulk modulus K0T was found to be 252 (±3) GPa, assuming that its pressure derivative K′0T is 4, by fitting a third order Birch‐Murnaghan equation of state. δAlOOH is thus the least compressible hydrous phase known with compressibility comparable to that of corundum and stishovite, confirming that this phase can be stable at the lower mantle conditions.
An Ocean Resonance in the Southeast Pacific
Authors: Webb David J. , de Cuevas Beverly A.
Published: October 2002

Satellite Altimeter observations of sea surface height show an extensive region of high variability in the Southeastern Pacific which previous studies have suggested is a Rossby wave trapped by topography. Here we investigate the feature using results from a high‐resolution global ocean model. We calculate the empirical orthogonal modes and find that 29% of the SSH variability is due to a single mode. We correlate the time series of the mode with the local Ekman pumping and find that the correlation is largest when the wind curl is averaged over a region roughly the size of the mode. We calculate the response function relating the two time series and find that it is dominated by a resonance at zero frequency with a decay time of about two days. We conclude that the feature is a highly damped geostrophic mode of the ocean.
Satellite observations of long‐term changes in tropical cloud and outgoing longwave radiation from 1985 to 1998
Authors: Wang Pi‐Huan , Minnis Patrick , Wielicki Bruce A. , Wong Takmeng , Vann Lelia B.
Published: October 2002

Cloud vertical distributions and radiation data from satellites taken between 1985 and 1998 were analyzed to determine the impact of clouds on outgoing longwave radiation (OLR) in the Tropics. Clouds with a 1‐μm optical depth greater than 0.025 above 12 km decreased, while those below 12 km increased. The OLR mean and decadal trend were 254 Wm−2and 3.9 Wm−2/decade, respectively. The mean cloud and OLR results were used to derive a value of 0.36 for the tropical mean cloud longwave effective emissivity. Changes in cloud vertical distributions account for 40% of the OLR trend. A change in cloud effective emissivity of −0.026/decade could account for the remainder of the OLR changes. These changes suggest reduced mean cloud opacity, a drier troposphere, and a strengthened large‐scale circulation in the Tropics during the period.
Tropical nitric acid clouds
Authors: Hervig Mark , McHugh Martin
Published: October 2002

The presence of nitric acid clouds near the tropical tropopause was proposed over a decade ago, although little has been learned about them since. Particle extinction measurements at three wavelengths from the Halogen Occultation Experiment offer compelling evidence for the existence of nitric acid clouds near the tropical tropopause. Most of these clouds are consistent with nitric acid trihydrate, and a small fraction can be explained by liquid ternary H2SO4‐H2O‐HNO3 aerosols.
A dual‐beamwidth radar method for measuring atmospheric turbulent kinetic energy
Authors: VanZandt T. E. , Nastrom G. D. , Furumoto J. , Tsuda T. , Clark W. L.
Published: October 2002

This paper introduces a new dual‐beamwidth (2BW) radar method for inferring the velocity variance σturb2 due to the turbulent kinetic energy density per unit mass. The 2BW method has the advantage of being much less sensitive than the standard single‐beamwidth (1BW) method to the necessary instrumental corrections of the observed velocity variance σobs2. We test and compare the 2BW and 1BW methods using σobs2 between 5.0 and 7.5 km MSL measured by the MU VHF radar near Shigaraki, Japan, with beams directed toward 10° zenith angle. We find that during periods of light winds the σturb2 profiles from the two methods agree well. But with wind speeds >30 m/s the 1BW values of σturb2 are about 25% larger than the 2BW values. With the 2BW method, typical values of σturb2 between 6.0 and 7.5 km MSL increased from ∼0.07 m2/s2 with winds of ∼2 m/s to ∼0.2 m2/s2 with winds between 30 and 60 m/s.
Anisotropic effects of non‐axial seismic wave propagation in foliated crustal rocks
Authors: Okaya David A. , Christensen Nikolas I.
Published: October 2002

Seismic wave propagation within the crust is usually in directions not parallel to inherent rock symmetry axes due to geologic dips of structures and/or oblique‐to‐arcuate raypaths. We use Christoffel equations and petrophysically measured velocities of crustal metamorphic rocks to examine anisotropic velocities and traveltime effects as functions of non‐axial propagation. P‐ and S‐wave velocities are trigonometrically weighted between fast and slow axial velocities. Averaging over a range of non‐axial angles yields effective velocities as encountered by through‐going crustal raypaths. Axial velocities cannot be simply used to quantify crustal anisotropic effects. The angular behavior of P‐wave delay and shear wave splitting are sensitive to VP measured diagonal to the material symmetry axes; this diagonal velocity controls the presence or absence of non‐axial shear wave singularities. These behavior help quantify the contributions of crustal rocks to observations of seismic anisotropy which can serve as proxies for crustal deformation.
Leakage of energetic particles from Jupiter's dusk magnetosphere: Dual spacecraft observations
Authors: Krupp N. , Woch J. , Lagg A. , Espinosa S. A. , Livi S. , Krimigis S. M. , Mitchell D. G. , Williams D. J. , Cheng A. F. , Mauk B. H. , McEntire R. W. , Armstrong T. P. , Hamilton D. C. , Gloeckler G. , Dandouras J. , Lanzerotti L. J.
Published: October 2002

For the first time, two spacecraft, Galileo and Cassini, observed Jupiter's magnetosphere simultaneously for nearly half a year between October 2000 and March 2001. This provided an unprecedented opportunity to disentangle spatial and temporal aspects of the dynamics of the Jovian magnetosphere. In this paper we report new results on the source of the leakage of energetic particles (electrons with energy 15 keV to several MeV and ions with energy > 30 keV) from the dusk side of the magnetosphere. The dual spacecraft measurements show clearly that magnetospheric particles leak directly into the interplanetary medium from the closed magnetosphere, and are the source for the “upstream” particle events [Baker et al., 1996; Zwickl et al., 1981; Krimigis, 1992; Haggerty and Armstrong, 1999; Anagnostopoulos et al., 1998] that have been reported from instruments during prior single spacecraft encounters with the planet. These events, consisting of high‐energy particles of Jovian origin, have been observed throughout the heliosphere [Baker and Van Allen, 1976] and their propagation has recently been modelled [Fichtner et al., 2000; Ferreira et al., 2001]. Jupiter then is an important contributor to the interplanetary charged particle fluxes, especially within an astronomical unit of the planet.
Self‐potential signals associated with variations of the hydraulic head during an infiltration experiment
Authors: Revil A. , Hermitte D. , Voltz M. , Moussa R. , Lacas J.‐G. , Bourrié G. , Trolard F.
Published: October 2002

A field experiment was performed to monitor the variations of the hydraulic head in the vicinity of a ditch during a water infiltration experiment and using the self‐potential method. The coupling between electric and hydraulic flows is electrokinetic in nature. The electrical signals are measured at the ground surface with a set of ten non‐polarisable Petiau (Pb/PbCl2) electrodes over a section perpendicular to the ditch. The electrical potential is linearly related to the depth of the water table, which is here quite shallow (between ∼1 to 2 m). A rough estimate of the electrokinetic coupling coefficient obtained in the field is ∼−10 mV per meter of hydraulic head (∼−1000 mV MPa−1 of pore fluid pressure). The order of magnitude of this estimate agrees with a laboratory experiment performed with a soil sample from the test site. The good correlation found between electrical potential and hydraulic head variations opens the door to direct tomography of hydraulic head fluctuations with many innovative applications in hydrogeology, especially because the potential depth to which this method could be applicable is high (several hundred meters).
Stratospheric ozone depletion at northern mid latitudes in the 21st century: The importance of future concentrations of greenhouse gases nitrous oxide and methane
Authors: Randeniya L. K. , Vohralik P. F. , Plumb I. C.
Published: October 2002

There is evidence that the halogen loading of the atmosphere has peaked and stratospheric ozone levels are expected to recover to pre‐1980 levels this century. However, N2O concentrations in the atmosphere are increasing, resulting in increasing levels of NOx in the stratosphere. In addition, the growth rate in the atmospheric methane burden has declined in recent years, leading to the suggestion that methane emissions have stabilized. A 2‐D chemical transport model is used to calculate stratospheric ozone from 2000 to 2100 for a range of IPCC scenarios. The model predicts that mid‐latitude stratospheric ozone will recover only partially towards pre‐1980 levels over the next 50 years, but will then decline, largely due to increases in stratospheric NOx. If greenhouse gas mitigation strategies result in lower future methane levels, mid‐latitude stratospheric ozone levels in 2100 are predicted to be lower than current values, particularly in late summer and autumn.
Spaceborne measurements of atmospheric CO2 by high‐resolution NIR spectrometry of reflected sunlight: An introductory study
Authors: Kuang Zhiming , Margolis Jack , Toon Geoffrey , Crisp David , Yung Yuk
Published: October 2002

We introduce a strategy for measuring the column‐averaged CO2 dry air volume mixing ratio from space. It employs high resolution spectra of reflected sunlight taken simultaneously in near‐infrared (NIR) CO2 (1.58‐μm and 2.06‐μm) and O2 (0.76‐μm) bands. Simulation experiments, show that precisions of ∼0.3–2.5 ppmv for can be achieved from individual clear sky soundings for a range of atmospheric/surface conditions when the scattering optical depth τs is less than ∼0.3. When averaged over many clear sky soundings, random errors become negligible. This high precision facilitates the identification and correction of systematic errors, which are recognized as the most serious impediment for the satellite measurements. We briefly discuss potential sources of systematic errors, and show that some of them may result in geographically varying biases in the measured . This highlights the importance of careful calibration and validation measurements, designed to identify and eliminate sources of these biases. We conclude that the 3‐band, spectrometric approach using NIR reflected sunlight has the potential for highly accurate measurements.
Exhumation rates of high pressure metamorphic rocks in subduction channels: The effect of Rheology
Authors: Gerya T. V. , Stöckhert B.
Published: October 2002

Exhumation of high‐pressure metamorphic rocks can take place with typical plate velocities of cm/year. This is consistent with a model of forced flow in a subduction channel. The (micro)structural record of exhumed metamorphic rocks indicates that stresses are generally too low to drive deformation of the bulk material by dislocation creep, according to a power‐law rheology. Instead deformation appears to be localized in low‐strength shear zones, and is dominated by dissolution precipitation creep or fluid assisted granular flow, implying a Newtonian rheology. 1D modeling shows that the effective rheology of the material in the subduction channel has a significant influence on the rate of exhumation. When the subduction flux either equals or exceeds the return flux, the maximum exhumation rate for Newtonian behavior of the material is at least twice as high (∼1/3 of the subduction burial rate) compared to that for power‐law creep (∼1/6 of the subduction burial rate).
The mechanical and thermal structure of Mercury's early lithosphere
Authors: Watters Thomas R. , Schultz Richard A. , Robinson Mark S. , Cook Anthony C.
Published: October 2002

Insight into the mechanical and thermal structure of Mercury's early lithosphere has been obtained from forward modeling of the largest lobate scarp known on the planet. Our modeling indicates the structure overlies a thrust fault that extends deep into Mercury's lithosphere. The best‐fitting fault parameters are a depth of faulting of 35 to 40 km, a fault dip of 30° to 35°, and a displacement of ∼2 km. The Discovery Rupes thrust fault probably cut the entire elastic and seismogenic lithosphere when it formed (∼4.0 Gyr ago). On Earth, the maximum depth of faulting is thermally controlled. Assuming the limiting isotherm for Mercury's crust is ∼300° to 600°C and it occurred at a depth of ∼40 km, the corresponding heat flux at the time of faulting was ∼10 to 43 mW m−2. This is less than old terrestrial oceanic lithosphere but greater than the present heat flux on the Moon.
Precipitation variability associated with the North American Monsoon in the 20th century
Authors: Kim Jinwon
Published: October 2002

An analysis of century‐long precipitation data shows that the interseasonal and continental‐scale variations of precipitation anomalies associated with interannual variations of the North American Monsoon (NAM) are notably different between the two periods of 1901–1962 and 1963–1994. In Arizona‐New Mexico (AZ‐NM), wet (dry) summers are preceded by dry (wet) winters only after 1962. Another characteristic of the NAM variability, a summer rainfall pattern of wetter (drier) AZ‐NM, and drier (wetter) Great Plains (GP), is observed only after 1962, as well. The strongest contrast in summer rainfall anomalies appears between AZ‐NM and the southeastern U.S. for 1901–1962, while it appears between AZ‐NM and the GP for 1963–1994. For the period after 1962, the precipitation variability obtained here show the same features found in earlier studies. Causes of the observed changes in the precipitation characteristics around 1960 are not clear due to a lack of large–scale atmospheric and oceanic data before 1950.
Systematic differences between radiosonde instruments
Authors: Lait Leslie R.
Published: October 2002

Deviations of radiosonde geopotential heights from the zonal mean are examined. In the summer Northern Hemisphere stratosphere, systematic differences are found between radiosonde instrument types. Persistent meridional wind anomalies, approximately constant in magnitude and fixed in location, have previously been reported in the summer stratosphere, and one such anomaly over Europe is found to be co‐located with boundaries between regions in which differing types of radiosonde instruments are used. The magnitude and orientation of the radiosonde geopotential height biases are consistent with the wind anomalies. Because the overall winds tend to be light in this region and season, these wind anomalies can represent significant perturbations of the flow and must be considered when interpreting the results of trajectory and diagnostic studies.
A switch from Si(OH)4 to NO3− depletion in the glacial Southern Ocean
Authors: Brzezinski Mark A. , Pride Carol J. , Franck Valerie M. , Sigman Daniel M. , Sarmiento Jorge L. , Matsumoto Katsumi , Gruber Nicolas , Rau Greg H. , Coale Kenneth H.
Published: October 2002

Phytoplankton in the Antarctic deplete silicic acid (Si(OH)4) to a far greater extent than they do nitrate (NO3−). This pattern can be reversed by the addition of iron which dramatically lowers diatom Si(OH)4:NO3− uptake ratios. Higher iron supply during glacial times would thus drive the Antarctic towards NO3− depletion with excess Si(OH)4 remaining in surface waters. New δ30Si and δ15N records from Antarctic sediments confirm diminished Si(OH)4 use and enhanced NO3− depletion during the last three glaciations. The present low‐Si(OH)4 water is transported northward to at least the subtropics. We postulate that the glacial high‐Si(OH)4 water similarly may have been transported to the subtropics and beyond. This input of Si(OH)4 may have caused diatoms to displace coccolithophores at low latitudes, weakening the carbonate pump and increasing the depth of organic matter remineralization. These effects may have lowered glacial atmospheric pCO2 by as much as 60 ppm.
Effect of lithosphere thickness heterogeneities in controlling rift localization: Numerical modeling of the Oslo Graben
Authors: Pascal C. , van Wijk J. W. , Cloetingh S. A. P. L. , Davies G. R.
Published: October 2002

We present 2‐D thermo‐mechanical and numerical modeling at lithospheric scale to assess the impact of pre‐existing lithosphere thickness contrast on rift localization. The results of the modeling suggest that thickness heterogeneity was responsible for focussing rifting and passive asthenospheric upwelling in the Permo‐Carboniferous Oslo Graben at the western margin of the Fennoscandian Shield. These findings are consistent with inferences from recent studies showing that both the crust‐mantle boundary and the base of the lithosphere are and were deeper at the eastern margin of the Oslo Graben, resulting in contrasting crust and lithosphere thickness.
Do deep ocean temperature records verify models?
Authors: Lindzen Richard S.
Published: October 2002

Recent papers show that deep ocean temperatures have increased somewhat since 1950, and that the increase is compatible with the predictions of coupled GCMs. The inference presented is that this degree of compatibility constitutes a significant test of the models. The present paper assumes that the measurements and their analysis are correct, and uses a highly simplified coupled model (i.e., an energy balance model with a mixed layer diffusive ocean) to examine whether deep ocean temperature behavior from 1950 to 2000 actually distinguishes between models of radically different sensitivity to doubled CO2. It is found that whenever models are tuned with additional forcing (for example, from aerosols) so as to replicate observed global mean temperature, the warming of the ocean temperature is largely independent of model sensitivity. There is a modest dependence on ocean diffusivity with models' behavior characteristic of large diffusivity while observations are more characteristic of low diffusivity. However, the distinctions appear to lie within observational uncertainty. There is little reason to assume that more realistic models will behave very differently in this regard. Therefore, we conclude that the behavior of deep ocean temperatures is not a test of model sensitivity, but rather a consequence of having the correct global mean surface temperature time history.
Numerical study of boundary layer ozone transport and photochemical production in east Asia in the wintertime
Authors: Zhang Meigen , Uno Itsushi , Sugata Seiji , Wang Zifa , Byun Daewon , Akimoto Hajime
Published: October 2002

The transport and chemical transformation of boundary layer ozone in east Asia in January 1997 was investigated using the Models‐3 Community Multiscale Air Quality (CMAQ) modeling system with meteorological fields calculated by the Regional Atmospheric Modeling System (RAMS). The predicted ozone concentrations were compared with ground‐level observations at four remote sites in Japan and it was found that the model reproduces many of the important features in the observations. Examination of several high ozone episodes indicates that elevated ozone levels are found in association with continental outflow. Net ozone production is found to occur during the daytime over the lower marine atmosphere, and this is also evident from the observations, demonstrating the critical role of the rapid transport of ozone precursors from the Asian continent. An analysis of the ozone budget indicates that the supply and loss of boundary layer ozone in east Asia in winter are dominated by photochemistry.
Rate dependence of AE activity during frictional sliding
Authors: Yabe Yasuo
Published: October 2002

A velocity‐step test was performed to examine effects of the macroscopic sliding‐rate on AE activity during steady‐state frictional sliding on a pre‐cut fault in a granite sample. Both the amplitude‐frequency relation and the number of AE events per unit displacement changed in response to a change in the macroscopic sliding‐rate. Both the AE activity and its rate‐dependence evolved with sliding. The rate dependence of cumulative seismic energy calculated from the AE activity shows a positive correlation to that of friction coefficient, suggesting that the rate dependence of seismic energy is one of the origins of rate‐dependent friction, because the seismic energy is a part of frictional energy‐loss. Further, the rate dependence of seismic energy is much larger than that of friction, meaning that a ratio of seismic energy to frictional energy‐loss depends on the macroscopic sliding rate.
Monitoring the explosive activity of the July–August 2001 eruption of Mt. Etna (Italy) by ash characterization
Authors: Taddeucci Jacopo , Pompilio Massimo , Scarlato Piergiorgio
Published: October 2002

During the summer 2001 eruption of Mt. Etna, Italy, we developed a method for monitoring explosive activity through the study of airborne ash. The method is based on two routine and fast techniques for ash characterization: i) component analysis, that quantifies the proportion of juvenile particles, crystals, and non‐juvenile lithics in the ash; ii) Scanning Electron Microscope semi‐quantitative description of the morphology of ash particles. With these techniques we daily analyzed airborne ash from the eruption plume. Temporal evolution of particle shape and vesicularity, and of component proportion in the ash, documented initial crater excavation by hydromagmatic explosions, strong magmatic activity due to volatile exsolution, and final fragmentation of a cooling top of magma column. Favorable conditions of the studied eruption allowed validation of these results by comparison with other monitoring techniques. We also evaluate the applicability of the method to other cases, as well as its limits.
Seismic image and its implications for an earthquake swarm at an active volcanic region off the Miyake‐jima–Kozu‐shima, Japan
Authors: Kodaira Shuichi , Uhira Kohichi , Tsuru Tetsuro , Sugioka Hiroko , Suyehiro Kiyoshi , Kaneda Yoshiyuki
Published: October 2002

An intensive earthquake swarm, which is proposed to be attributed to the magmatic activity, has continued in more than six months around the Miyake‐jima–Kozu‐shima. A wide‐angle seismic survey was conducted immediately above the swarm. The purpose of this study is to map the seismic velocity structure of the swarm area, and to investigate structural evidence indicating magmatic activity. From the result of first arrival refraction tomography, we found a 5–8% decrease in P‐wave velocity surrounding the swarm. A depth migration of the intra‐crustal reflection phase also shows an existence of a reflector immediately below the swarm (10–13 km depth). Compared with the seismic imaging, geodetic data and earthquake focal mechanisms, the intra‐crustal reflector we found might be the top of magmatic body which has caused the earthquake swarm between Miyake‐jima and Kozu‐shima.
Tomographic images and 3D earthquake locations of the seismic swarm preceding the 2001 Mt. Etna eruption: Evidence for a dyke intrusion
Authors: Patane Domenico , Chiarabba Claudio , Cocina Ornella , De Gori Pasquale , Moretti Milena , Boschi Enzo
Published: October 2002

On July, 12, 2001, Mt. Etna experienced a sudden increase of seismic activity heralding one of the most intense eruptions of the past 30 years. Between July 12 and July 18, when the eruption started, thousands of small magnitude earthquakes occurred and were recorded by a dense seismic network run by the Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania (INGV‐CT). Hypocentral depths of earthquakes were very shallow, mostly located above 3 km b.s.l. and clustered near the summit area. The high quality seismic dataset gives us the unique opportunity to study the process of magma migration before the eruption. In this study we present the three‐dimensional earthquake locations and the velocity structure obtained by a tomographic inversion. The shallowness of seismicity allowed us to enhance the details of the structure beneath the summit craters, in a volume poorly defined by previous tomographic studies. The presence of a high Vp‐body previously observed at Mt. Etna is confirmed at shallow depth beneath the southeastern part of the summit area. The earthquakes preceding the eruption onset concentrated at its western border. A low Vp/Vs anomaly is found at 0–1 km depth, just at the top of the volume where the magma intruded before the eruption. This anomalous zone can be considered as molten material wealthy in gas. The relocated seismicity occurs in a cylinder below the vents activated along the fracture system and exhibited an upward migration until the eruption. All these results show evidence for the emplacement of a near‐vertical dyke striking about N‐S and a few kilometres south of the summit craters.
Towards evaluating the viscosity of the Earth's outer core: An experimental high pressure study of liquid Fe‐S (8.5 wt.% S)
Authors: Rutter Michael D. , Secco Richard A. , Uchida Takeyuki , Liu Hongjian , Wang Yanbin , Rivers Mark L. , Sutton Stephen R.
Published: October 2002

In‐situ high pressure viscosity measurements, using synchrotron X‐ray radiography, have been carried out on liquid Fe‐S (8.5 wt.% S) at pressures up to 6 GPa and at 1823 K. Here we show that (i) the effect of pressure on the isothermal viscosity is substantial, with an apparent activation volume of 5.8 cm3/mol; and (ii) viscosity is constant along the pressure dependent melting boundary. Assuming the independence of viscosity along the melting boundary up to core pressures, our results yield a viscosity for the Earth's outer core, at the inner core boundary, of 1.6 × 10−2 Pa s. On this basis, we present a revised viscosity profile across the outer core.
Remote sensing of non‐aerosol absorption in cloud free atmosphere
Authors: Kaufman Yoram J. , Dubovik Oleg , Smirnov Alexander , Holben Brent N.
Published: October 2002

Knowledge of the absorption of sunlight by atmospheric gases, aerosols and clouds is key to understanding climate and its variation. Several studies suggested that clouds absorb sunlight significantly more than what models predict. Other studies suggested that the anomalous absorption is present in cloud‐free conditions. Here we measure absorption in cloud free atmosphere using the Aerosol Robotic Network (AERONET). Measurements of attenuation of direct sunlight are used to derive extinction optical thickness and sky measurements to derive scattering optical thickness, Residual extinction for zero scattering, cannot be caused by aerosols or known gases and would be associated with the cloud free absorption anomaly. The anomalous absorption, if exists, is assumed not to correlate with the presence of aerosol. The measurements, taken for several years in locations around the world, show that in the atmospheric windows 0.44, 0.67, 0.87 and 1.02 μm the only significant absorbers in cloud free atmosphere is aerosol and ozone. Non‐aerosol absorption, defined as spectrally independent or smoothly variable, was found to have an optical thickness smaller than 0.002 ± 0.003, thereby, absorption of sunlight smaller than 1W/m2.
The effect of water on the 410‐km discontinuity: An experimental study
Authors: Smyth Joseph R. , Frost Daniel J.
Published: October 2002

In order to evaluate the effect of H on the pressure and transition interval of the olivine‐wadsleyite transformation, synthesis experiments were carried out in hydrous and anhydrous peridotite compositions at 1400°C. Under hydrous, near‐saturated conditions, the pressure of the transition is 1.0 ± 0.5 GPa lower than under anhydrous conditions. In addition, the two‐phase interval appears to broaden from about 0.4 GPa (12 km) in the anhydrous system to as much as 1.3 GPa (40 km) in the hydrous system. Under hydrous conditions the spatial distribution of olivine and wadsleyite appears to be controlled by H diffusion. Extrapolating previously measured diffusion coefficients for H in olivine and in liquids, it appears that H diffusion driven by gravitational equilibration may serve to narrow the transition interval between olivine and wadsleyite.
Effect of water on olivine‐wadsleyite phase boundary in the (Mg, Fe)2SiO4 system
Authors: Chen Jiuhua , Inoue Toru , Yurimoto H. , Weidner Donald J.
Published: October 2002

The phase boundary between San Carlos olivine and its high pressure phase, wadsleyite, have been studied comparatively in dry and water saturated condition. By comparing saturated and dry samples from the same experimental run, we determine that both boundaries of the two‐phase coexisting loop shift towards lower pressure or lower iron content, and the pressure width of the loop decreases to 0.3 GPa under saturated conditions at 1473 K. Thus, the presence of water in the Earth's mantle will sharpen the 410‐kilometer seismic discontinuity, shallow the depth of the discontinuity, and reduce the velocity jump across the discontinuity.
Lithosphere and asthenosphere of the Tien Shan imaged by S receiver functions
Authors: Oreshin Serge , Vinnik Lev , Peregoudov Dmitry , Roecker Steve
Published: October 2002

The S receiver function technique was applied to the recordings from 36 broad‐band stations in the Tien Shan. The results reveal a pronounced difference in the properties of the lithosphere‐asthenosphere of the Tien Shan and those of the neighboring platforms. Beneath the Tien Shan, an upper‐mantle lid with an S velocity of about 4.5 km/s is underlain at a depth of about 90 km by a low‐velocity zone, where the S velocity drops to 4.1–4.2 km/s. Trends of P and S travel time residuals are consistent with the presence of melt or other liquids in this zone. There is no evidence of any similar layer beneath the platforms. The crust is 55–65 km thick beneath most of the Tien Shan and 45 km below the platforms, although it thins to about 45 km near the Naryn basin in the central Tien Shan.
Evidence of scattering of tropospheric radiation by PSCs in mid‐IR limb emission spectra: MIPAS‐B observations and KOPRA simulations
Authors: Höpfner M. , Oelhaf H. , Wetzel G. , Friedl‐Vallon F. , Kleinert A. , Lengel A. , Maucher G. , Nordmeyer H. , Glatthor N. , Stiller G. , Clarmann T. v. , Fischer H. , Kröger C. , Deshler T.
Published: October 2002

Polar stratospheric clouds (PSCs) were observed by the high resolution mid infrared Michelson Interferometer for Passive Atmospheric Sounding, Balloon borne version (MIPAS‐B), on a flight from Kiruna/Sweden on January 11, 2001. Highly resolved spectral features in the limb measurements could only be explained by tropospheric radiation scattered into the line of sight by large PSC particles. Furthermore, model calculations showed that for PSCs with particles of radius ≥1 μm, a significant part of the broadband continuum radiance signal is due to scattering. Inclusion of scattering in the retrieval process resulted in reasonable values of otherwise largely overestimated PSC volume density profiles.
The role of stratospheric resolution in simulating the Arctic Oscillation response to greenhouse gases
Authors: Gillett Nathan P. , Allen Myles R. , Williams Keith D.
Published: October 2002

The Arctic Oscillation index has increased significantly over the past forty years, and such an increase has been simulated in response to greenhouse gas increases in several climate models. However, it has been suggested that an atmospheric model with an upper boundary in the upper stratosphere or mesosphere is required to simulate a realistic response, and that predictions made with standard climate models are hence unreliable. Here we show that a climate model with a 30‐km upper boundary shows no increase in its surface Arctic Oscillation response to doubled carbon dioxide when its upper boundary is raised to 80 km. Neither model version shows a significant Arctic Oscillation response to stratospheric ozone depletion.
A new algorithm for retrieving GPS radio occultation total electron content
Authors: Syndergaard Stig
Published: October 2002

A new algorithm for retrieving the relative ionospheric satellite‐to‐satellite total electron content during Global Positioning System (GPS) radio occultations is proposed. The algorithm consists of a linear combination of the L1 and L2 excess phase data using precise orbit information of the transmitter and receiver. The combination eliminates the effects of refractive bending and dispersion to first order. Simulations, representative of solar maximum conditions, show that using the “traditional” combination of the L1 and L2 phases, bending and dispersion may cause a systematic residual error of up to 20 TECU. Using only the L1 excess phase, the corresponding maximum residual error is about 7 TECU. The proposed combination results in a residual error due to bending and dispersion less than 0.1 TECU. Uncertainty in satellite orbit determination, as well as an unmodeled residual related to the geomagnetic field, result in a total systematic error of 1–2 TECU.
On moment‐length scaling of large strike slip earthquakes and the strength of faults
Authors: Romanowicz B. , Ruff L. J.
Published: October 2002

Several large strike slip earthquakes have occurred in various tectonic settings in the past 5 years, adding well documented data to the global collection of moment and length estimates for such earthquakes. Based on this augmented dataset, we reexamine the controversial issue of scaling of seismic moment with length of rupture. We find that the global dataset of large strike‐slip earthquakes follows a bi‐modal distribution. Most oceanic and/or intraplate strike‐slip earthquakes have stress drops that are ∼5 times larger than interplate continental ones. When distinguishing these two classes, the scaling is compatible with that predicted by simple dislocation theory.
A telescopic and microscopic view of a magnetospheric substorm on 31 March 2001
Authors: Baker D. N. , Ergun R. E. , Burch J. L. , Jahn J.‐M. , Daly P. W. , Friedel R. , Reeves G. D. , Fritz T. A. , Mitchell D. G.
Published: October 2002

On March 31, 2001 at ∼0635 UT when the CLUSTER constellation was near local midnight and at ∼4 RE geocentric distance, sensors observed an energetic electron injection event associated with a strong (AE ∼ 1200 nT) magnetospheric substorm. Geostationary spacecraft 1991‐080 located at ∼20 LT also saw an abrupt electron injection event at ∼0630 UT and FAST spacecraft instruments (∼19 LT) detected a powerful set of magnetic field, electric field, and energetic plasma signatures at ∼0637 UT. The energetic neutral atom imaging experiments onboard the IMAGE spacecraft detected an injection of substorm‐produced ions in the pre‐midnight sector commencing at ∼0630 UT. Electron injection signatures at the four separate CLUSTER locations allow us to infer the location, speed, and direction of the substorm injection boundary. Hence, the CLUSTER (and IMAGE) telescope‐microscope combination is a long‐sought realization of a major magnetospheric research objective and shows the power of localized multi‐point measurements from CLUSTER.
An ENSO predictor of dust emission in the southwestern United States
Authors: Okin Gregory S. , Reheis Marith C.
Published: October 2002

Here we show that there is a significant relationship between Nino 3.4 ENSO anomaly (Dec–Jan average) and precipitation in the southwestern United States. This contributes to increased frequency of dust events in the years following strong La Niña and El Niño years. High probabilities (60%–100%) exist for an elevated frequency of dust events in years when the ENSO anomaly, annual precipitation, or annual P/PE falls below the 10th percentile. This analysis provides a quantitative framework in which to evaluate the expected effects of climate change on this and other arid regions.
Hindcasting the NAO using diabatic forcing of a simple AGCM
Authors: Peterson K. Andrew , Greatbatch Richard J. , Lu Jian , Lin H. , Derome J.
Published: October 2002

A primitive equation dry atmospheric model with a rudimentary representation of the model physics is used to hindcast the winter NAO using diabatic forcing diagnosed from NCAR/NCEP reanalysis data in the period 1949–1999. Using ensembles of experiments we are able to reproduce the observed NAO index in the ensemble mean with a correlation of 0.79. By prescribing time dependent forcing only in the tropics (30°S–30°N), or only in the extra‐tropics, we show that the recent upward trend in the NAO is related to tropical forcing. The implication is that coupling with the mid‐latitude or Arctic ocean is not important for the trend. The model also exhibits the recent eastward shift in the sea level pressure signature of the interannual NAO variability and shows that this is associated with non‐linear dynamical processes.
Post‐glacial slip history of the Sparta fault (Greece) determined by36Cl cosmogenic dating: Evidence for non‐periodic earthquakes
Authors: Benedetti Lucilla , Finkel Robert , Papanastassiou Dimitris , King Geoffrey , Armijo Rolando , Ryerson Frederick , Farber Daniel , Flerit Frederic
Published: October 2002

Using36Cl cosmic ray exposure dating we obtained continuous exposure histories for 7–12 m‐high limestone surfaces at two sites (10 km apart) on the Sparta normal fault scarp. As each major earthquake adds new surface to the cumulative scarp exposing new material to cosmic‐ray bombardment these exposure histories allow the slip history to be constrained. The results show that an earthquake occurred on this fault 2800 ± 300 yr ago. We infer that this is the seismic event that destroyed ancient Sparta in 464 B.C. Four earlier earthquakes ruptured the Sparta fault in the last 13 ka with similar slip amplitudes of about 2 m and with time intervals ranging from 500 yr to 4500 yr. The observations also confirm that the Sparta scarp is post‐glacial, supporting the hypothesis that similar scarps elsewhere in the Mediterranean region have a comparable age. The absence of any event since 464 B.C. could suggest a future event is imminent. However, the irregularity of earthquake time intervals could also be due to changes of loading with important consequences for the mechanics of continental deformation.
The equatorial counter electrojet: Part of a worldwide current system?
Authors: Gurubaran S.
Published: October 2002

The method of natural orthogonal components was applied to the ground geomagnetic data in the Central Asian sector (72–83°E), during the summer months of 1995, in an attempt to identify additional current systems that are superposed on the normal Sq current vortex and related to the equatorial counter electrojet (CEJ). The principal components, when examined in equivalent current representation, provide useful insights into the behavior of ionospheric current systems on different days. Statistical analyses performed in the present work suggest a possible relationship between the CEJ field and the noontime D variation observed at low latitudes. The results are in conformity with an earlier global simulation model.
Shift in the summer rainfall over the Yangtze River valley in the late 1970s
Authors: Gong Dao‐Yi , Ho Chang‐Hoi
Published: October 2002

The summer rainfall over the middle‐lower valley of the Yangtze River and over the whole eastern China experienced a notable regime shift in about 1979. This change is consistent with a simultaneous jump‐like change in the 500 hPa geopotential height (Φ500) over the northern Pacific. The rainfall over the Yangtze River valley is closely related to the Φ500 averaged over the area 20°–25°N, 125°–140°E, with a correlation coefficient of 0.66 for the period 1958–1999. Since 1980, the subtropical northwestern Pacific high (SNPH) has enlarged, intensified, and extended southwestward. The changes in the SNPH are strongly associated with the variations of the sea surface temperatures (SSTs) of the eastern tropical Pacific and tropical Indian Ocean. The anomalies of these SSTs, responsible primarily for the shift of the summer rainfall over the Yangtze River through the changes in SNPH, precede the Φ500 signals with different leading times.
Atmospheric CO2 retrieved from ground‐based near IR solar spectra
Authors: Yang Zhonghua , Toon Geoffrey C. , Margolis Jack S. , Wennberg Paul O.
Published: October 2002

The column‐averaged volume mixing ratio (VMR) of CO2 over Kitt Peak, Arizona, has been retrieved from high‐resolution solar absorption spectra obtained with the Fourier transform spectrometer on the McMath telescope. Simultaneous column measurements of CO2 at ∼6300 cm−1 and O2 at ∼7900 cm−1 were ratioed to minimize systematic errors. These column ratios were then scaled by the mean O2 VMR (0.2095) to yield column‐averaged vmrs of CO2. These display similar behavior to the Mauna Loa in situ surface measurements. During the period 1977–1995, the column‐averaged mixing ratio of CO2 increased at an average rate of 1.49 ± 0.04 ppmv/yr with seasonal variations of ∼7 ppmv peak‐to‐peak. Our retrievals demonstrate that this remote technique is capable of precisions better than 0.5%.
An oceanic teleconnection between the equatorial and southern Indian Ocean
Authors: Schouten M. W. , de Ruijter W. P. M. , van Leeuwen P. J. , Dijkstra H. A.
Published: October 2002

Sequences of Kelvin and Rossby waves are found to rapidly carry sea surface height anomalies across the Indian Ocean, and have an impact on Indian to Atlantic interocean exchange. Satellite altimeter data reveal an oceanic teleconnection between equatorial winds and variability of the interocean exchange. Four times per year, we observe an equatorial Kelvin wave to hit Indonesia, forced by monsoon variability. The signal then propagates southward along the Indonesian coast and triggers Rossby waves that propagate westward across the subtropical Indian Ocean. On reaching the Madagascar and Mozambique Channel regions, large rings form at the same four per year frequency. These drift towards the Agulhas retroflection where they control the shedding of Agulhas rings. Disturbances of this pin‐ball‐like propagating signal can be traced from Indian Ocean Dipole/El Niño events in 1994 and 1997/1998, to decreases of Indian‐Atlantic ocean exchange by Agulhas rings over two years later.
Time‐independent and time‐dependent behaviour of high‐latitude flux bundles at the core‐mantle boundary
Authors: Bloxham Jeremy
Published: October 2002

Using a numerical dynamo model, we examine whether quasi‐stationary high latitude flux bundles which are observed in the geomagnetic field over the last 300 years, and possibly over much longer time periods, result from thermal core‐mantle interactions. We do so by imposing lateral heat flux variations at the core‐mantle boundary based upon the dominant pattern of seismic heterogeneity in the lowermost mantle. We find that the time‐averaged field then has a similar arrangement of flux bundles to that observed during the last few hundred years. However, the field is time‐dependent, and this arrangement of flux bundles is not a feature of the field at all times.