bluuebunny/crossref_metadata_2025 huggingface dataset:
Atmospheric pressure‐forced subinertial variations in the transport through the Korea Strait
Authors: Lyu Sang Jin , Kim Kuh , Perkins Henry T.
Published: October 2002

Transport variations with periods of 3 ∼ 5 days have been measured in the Korea (Tsushima) Strait by cross‐strait cable voltage fluctuations and by direct, long‐term measurement. Here we show that these variations can be explained in part by large‐scale atmospheric pressure fluctuations over the East (Japan) Sea. First, using basin‐wide averages of atmospheric pressure and sea surface height we show that sea surface height in the East Sea is not in isostatic equilibrium with atmospheric pressure, and that the imbalance is correlated with transport fluctuations. Second, we use a simple model to estimate the relationship between these quantities. The model displays a Helmholtz‐like resonance in the observed range of periods and is in reasonable agreement with the observed transport variations.
Theoretical models of intermediate and inverse AMS fabrics
Authors: Ferré Eric C.
Published: October 2002

Multi‐domain magnetites display a normal anisotropy of magnetic susceptibility (AMS) fabric where grain shape axes coincide with AMS axes. By contrast, single‐domain magnetite has an inverse magnetic fabric where magnetic axes are interchanged. The mixing of normal and inverse magnetic fabrics results in intermediate fabrics. Theoretical models for intermediate fabrics consider all combinations of normal and inverse fabrics. The minimum amount of inverse component required for intermediate fabrics to form is about 20% in the case of prolate normal (T = −0.50) and prolate inverse (T = −0.42) components. Such a small amount of inverse component may not be noticed. The anisotropy resulting from intermediate fabrics is lower than that of the normal or inverse contribution to AMS. This suggests that whenever intermediate fabrics occur neither the shape factor nor the degree of anisotropy relate to strain in a simple way.
Relationship between easterly waves and mesoscale convective systems over the Sahel
Authors: Mathon Vincent , Diedhiou Arona , Laurent Henri
Published: October 2002

Relationship between Sahelian mesoscale convective systems and easterly waves is studied at various time and space scales during 5 rainy seasons (1st July–15th September 1990–1994). This study focuses on a sub‐population of MCSs called organised convective systems (OCS) which account for most of the rainfall. Wave activity periods are detected by spectral analyses on the 700 hPa meridional wind component, information on the convective systems is derived from an automatic tracking algorithm and rainfall data of the EPSAT‐Niger experiment. We observe a modulation of OCS cloud cover at synoptic‐scale during easterly wave activity, with an increase of the cloud cover in and ahead of the trough but OCS rainfall efficiency is maximum behind of the wave trough. At seasonal scale, OCS number and cloud cover distributions are not significantly affected by easterly wave occurrences, which means that the latter are not directly associated to the interannual variability of rainfall.
Orbital dynamics about a slowly rotating asteroid
Authors: Howard J. E. , Wilkerson T. D. , Cantrell J. N.
Published: October 2002

We analyze orbital stability of satellites (moonlet, spacecraft) near a slowly rotating axisymmetric asteroid. Using simple point mass models as a guide, we discover an unstable region near the equatorial plane of an indented asteroid. The existence of stable/unstable regions is confirmed numerically for a realistic “peanut” model asteroid. The stable region is found to survive small asteroidal rotation about an axis of maximum moment of inertia. A simple semi‐empirical formula is found for the orbital tilt angle as a function of asteroid rotation speed. Implications for motion about realistic asteroids are discussed.
Relative contributions of crustal temperature and composition to controlling the depth of earthquakes in Southern California
Authors: Magistrale Harold
Published: October 2002

Control of the ∼13 km range of the maximum depth of earthquakes in southern California has been attributed previously to lateral variations in either crustal temperature or crustal rock composition. Here I compare heat flow (a proxy for crustal temperature), local maximum depths of earthquakes (d95), and best‐guess crustal rock compositions. Plotting heat flow versus d95 produces distinct trends for each rock composition, with each trend representing an isotherm marking the onset of plastic behavior. Offsets between the trends measure the differences in the plastic behavior temperatures of each rock composition; these offsets are comparable to the d95 variations with heat flow. Thus, crustal temperature and composition contribute about equally to the control of the maximum depths of earthquakes. The observed isotherm slopes imply vertical variations in crustal composition in addition to the lateral variations.
On the treatment of heterogeneous interfaces in soil
Authors: Schaudt K. J. , Morrill J. C.
Published: October 2002

At the interface between two dissimilar soils there are typically discontinuities in the water‐content and the gradients of both the flux and the soil matric potential (SMP). As the equation of motion for water depends on the gradient of flux, care must be taken to insure that the solution at such an interface obeys the relevant physical conditions. When a SMP‐based nodal average scheme is applied to a heterogeneous interface, a fundamental assumption (smoothness in the SMP profile) is violated, which typically leads to poor water balance and/or slow convergence with respect to grid size. We solve the water‐content based form of Richards' Equation using continuity in flux and soil matric potential as boundary conditions. Our scheme builds in excellent water balance and typically converges as fast as water‐content based schemes for homogeneous soils. We show results for infiltration into a dry, stratified soil.
A statistical estimate of daily mean temperature derived from a limited number of daily observations
Authors: Zaiki Masumi , Kimura Keiji , Mikami Takehiko
Published: October 2002

When a study is made of past climatic variations, it is preferable to obtain as long an instrumental record as possible. In Japan, the earliest official meteorological observations by JMA (Japan Meteorological Agency) date back to Hakodate in 1872. For about 130 years, the frequency and time of daily observation has varied. This is one of the major factors in creating data inhomogeneity. Accordingly, statistical estimation has been attempted to bridge the gap in daily mean temperatures caused by the limited number of daily observations. A Multiple Linear Regression Analysis was practically applied in the estimation of the daily mean temperature. The true value obtained from 24 hourly observational values (real daily mean temperature) was compared to a derived result using only three to four plus maximum and minimum daily observed temperatures. A high correlation between real values and estimated values was proven to exist.
Substorm onset times as derived from geomagnetic indices
Authors: Benkevitch L. V. , Lyatsky W. B. , Koustov A. V. , Sofko G. J. , Hamza A. M.
Published: October 2002

New magnetic parameters, dAE and dAO, are introduced to determine the preferential times for substorm onsets. dAE and dAO are time derivatives of the standard AE and AO indices. By analyzing long series of dAE and dAO we reveal their seasonal and diurnal variations, which, unlike those of the original AE and AO, show reasonable similarity. The preferential periods of substorm onsets are shifted from the spring and fall equinoxes; they occur around 0900–1800 UT for the winter months with maxima of occurrence in October‐November and February‐March. Substorms are rarer during summer months at all UT hours, which is in agreement with the results of Newell et al. [1996] that aurora are suppressed in sunlight. The substorm suppression during summer months corresponding to large total conductance of conjugate ionospheres is consistent with one of the potential substorm triggering mechanisms, the magnetosphere‐ionosphere feedback instability.
Polarization jet events and excitation of weak SAR arcs
Authors: Sazykin S. , Fejer B. G. , Galperin Yu. I. , Zinin L. V. , Grigoriev S. A. , Mendillo M.
Published: October 2002

Polarization Jet (PJ), also known as Sub‐Auroral Ion Drift (SAID), events are supersonic westward plasma drifts on the equatorward edge of the diffuse aurora in the evening and nighttime sector. Their optical F‐region signatures are weak 630.0 nm red arcs colocated with regions of fast convection. These weak arcs resemble Stable Auroral Red (SAR) arcs observed during the recovery phase of magnetic storms, but have lower intensities, shorter lifetimes, and occur without a significant heat flux from the magnetosphere. Previous model studies underestimated the brightness of weak SAR arcs. We present calculations showing that ion‐neutral collisional heating and ion composition changes during PJ events may be an additional source of 630.0 nm emission, and propose experimental tests that could verify our modeling results.
Improved mapping functions for atmospheric refraction correction in SLR
Authors: Mendes V. B. , Prates G. , Pavlis E. C. , Pavlis D. E. , Langley R. B.
Published: October 2002

We present two new mapping functions (MFs) to model the elevation angle dependence of the atmospheric delay for satellite laser ranging (SLR) data analysis. The new MFs were derived from ray tracing through a set of data from 180 radiosonde stations globally distributed, for the year 1999, and are valid for elevation angles above 3°. When compared against ray tracing of two independent years of radiosonde data (1997–1998) for the same set of stations, our MFs reveal submillimetre accuracy for elevation angles above 10°, representing a significant improvement over other MFs, and is confirmed in improved solutions of LAGEOS and LAGEOS 2 data analysis.
Dike emplacement forerunning the Etna July 2001 eruption modeled through continuous tilt and GPS data
Authors: Bonaccorso A. , Aloisi M. , Mattia M.
Published: October 2002

Late on the night of July 17, 2001, a lateral eruption started from the slopes of Mt. Etna. A 7 km long field of ground fractures opened between 13 and 20 July. The eruption ended on August 9, 2001 after emitting a lava volume of approximately 48 · 106 m3. A strong seismic swarm earthquake was recorded between July 12 and 17. The evolution leading up to the July crisis was monitored through continuous tilt and GPS measurements, which constrained the intrusion preceding the eruption in time, and inferred the position and geometry of the uprising dike. We modeled the marked ground deformation changes recorded in the days before the eruption onset. The result shows that a tensile crack with an opening dislocation of ca. 3 m, crossing the volcano edifice slightly southeast of the crater area, can explain the recorded deformation pattern. The location of the modeled tensile source fits the zone of the seismic swarm occurring during the magma uprising. The ground deformation pattern associated with the final uprising and its modeling suggest a very fast dike emplacement which appears different, both in terms of rapidity (only a few days) and source position, with respect to the sources modeled for the other lateral eruptions in the last twenty years.
Do large aftershocks decrease similarly to smaller ones?
Authors: Hosono Kohji , Yoshida Akio
Published: October 2002

It has been considered that the p value in the modified Omori formula does not depend on the cut‐off magnitude [Utsu et al., 1995], and large and small aftershocks decay similarly [Reasenberg and Jones, 1989a, 1989b]. Having investigated temporal decrease of aftershock activities of the 1995 Kobe and the 2000 Tottori earthquakes in detail, we found, however, that large aftershocks do not have a stable decay pattern, the p value in early periods is smaller than that obtained by the data in long periods which contain the later stage of the sequence. To say the point in another way or more clearly, number of large aftershocks in later periods is significantly short compared to that expected from the model that is obtained by fitting the decay in early time periods to the modified Omori formula. Preliminary analyses for several other aftershock sequences suggest that this is a common feature observed in all aftershock activities.
ULF waves in the solar wind as direct drivers of magnetospheric pulsations
Authors: Kepko L. , Spence H. E. , Singer H. J.
Published: October 2002

Global magnetospheric ULF pulsations with frequencies in the Pc 5 range (f = 1.7–6.7 mHz) and below have been observed for decades in space and on the Earth. Recent work has shown that in some cases these pulsations appear at discrete frequencies. Global cavity and waveguide modes have been offered as possible sources of such waves. In these models the magnetosphere is presumed to resonate globally at frequencies determined solely by its internal properties such as size, shape, field topology, mass density distribution, etc. We show in this work that upstream solar wind number density and dynamic pressure variations precede and drive compressional magnetic field variations at geosynchronous orbit. Furthermore, spectral analysis shows that wave power spectra in both the solar wind and magnetosphere contain peaks at the same discrete frequencies. Therefore, in contrast to the cavity mode hypothesis, we suggest that discrete ULF pulsations observed within the magnetosphere are at least sometimes directly driven by density oscillations present in the ambient solar wind. Finally, we comment on possible sources for such pulsations observed in the solar wind.
Is small scale convection responsible for the formation of thick igneous crust along volcanic passive margins?
Authors: Ghods Abdolreza
Published: October 2002

Boutilier and Keen [1999] showed that small scale convection may produce the observed thick igneous crust along volcanic passive margins provided that a non‐linear rheology is adopted and the viscosity of the upper mantle is increased suddenly after 132 km of continental crust extension. The sudden viscosity increase is justified by the melt induced dewatering of the upper mantle rocks. Through this comparative study, it is shown that inclusion of the pressure of the newly formed igneous crust into the melting model, and/or adopting a more realistic viscosity law, significantly reduces the thickness of igneous crust produced by Boutilier and Keen's models. Furthermore, it is shown that melt migration would narrow the width of the thick igneous crust. Results of this study show that small scale convection may not play a significant role in the formation of the observed thick igneous crust along volcanic passive margins.
Electromagnetic induction in the oceans and the anomalous behaviour of coastal C‐responses for periods up to 20 days
Authors: Kuvshinov Alexei V. , Olsen Nils , Avdeev Dmitry B. , Pankratov Oleg V.
Published: October 2002

Electromagnetic transfer functions at coastal sites are known to be strongly distorted by the conductivity of the seawater. This ocean effect is generally considered to be small for periods greater than a few days. We revise this statement by detailed and systematic model studies in the period range from 1 to 64 days, with subsequent comparison of the modelled and observed electromagnetic responses. The conductivity model consists of a radial symmetric (1‐D) section that is overlaid by a thin spherical surface shell, the conductance of which is compiled using the NOAA ETOPO topography/bathymetry and map of sediment thicknesses. The simulations were performed for spatial resolutions of the surface shell of 5° × 5°, 2° × 2° and 1° × 1°, respectively, and for two, continental and oceanic, underlying 1‐D conductivity models. The inducing source is described by the spherical harmonic P10 in dipole coordinates. Comparisons are made for the coastal geomagnetic observatories Apia, Hermanus, Kakioka, Kanoya, and Simosato where an anomalous behaviour of the local response has been previously detected. From the comparison of observed and modelled responses we conclude that peculiarities in the observed coastal responses in the period range from 1 to 20 days can be explained to a large amount by induction in the oceans. We show that correction for the ocean effect results in responses that are much better interpretable by 1‐D conductivity models compared to the uncorrected responses.
Seafloor hydrothermal systems driven by the serpentinization of peridotite
Authors: Lowell R. P. , Rona P. A.
Published: October 2002

Heat balance models predict that heat released upon serpentinization of peridotites can result in a wide range of hydrothermal venting temperatures. Temperatures ranging from a few to a few tens of °C are likely. Temperatures ∼300°C may be possible in conjunction with significant heat input from below, low fluid flow rate (≤10 kg/s), a high rate of serpentinization (≥100 kg/s), or some combination of these factors. The volume of fresh lithosphere accessible to serpentinization may limit the duration of an episode of hydrothermal venting when the serpentinization rate exceeds 10 kg/s. Hydrothermal venting driven by high rates of serpentinization may occur episodically as new reaction surfaces are made available by tectonic activity or crack propagation. Given the uncertainty of several parameters, the current episode of venting at the Lost City vent field on the Mid‐Atlantic Ridge may range from ∼102 to 104 years.
The Black Top Hat function applied to a DEM: A tool to estimate recent incision in a mountainous watershed (Estibère Watershed, Central Pyrenees)
Authors: Rodriguez Felipe , Maire Eric , Courjault‐Radé Pierre , Darrozes José
Published: October 2002

The Top Hat Transform function is a grey‐level image analysis tool that allows extracting peaks and valleys in a non‐uniform background. This function can be applied onto a grey‐level Digital Elevation Model (DEM). It is herein applied to quantify the volume of recent incised material in a mountainous Pyrenean watershed. Grey‐level Closing operation applied to the Present‐Day DEM gives a new image called “paleo” DEM. The Black Top Hat function consists in the subtraction of the “paleo” DEM with the Present‐Day DEM. It gives a new DEM representing all valleys whose sizes range between the size of the structuring element and the null value as no threshold is used. The calculation of the incised volume is directly derived from the subtraction between the two DEM's. The geological significance of the quantitative results is discussed.
Coseismic displacements of the MW= 6.1, July 9, 1998, Faial earthquake (Azores, North Atlantic)
Authors: Fernandes R. M. S. , Miranda J. M. , Catalão J. , Luis J. F. , Bastos L. , Ambrosius B. A. C.
Published: October 2002

On 9 July 1998 an earthquake occurred NE of Faial Island (Azores, North Atlantic). The Harvard CMT solution points to a sub‐vertical strike‐slip event corresponding to the strikes N241E and N151E. Here, we use GPS data to estimate the coseismic displacements and to constrain the geometry of the earthquake source. GPS observations collected between 1993 and 1999 are processed to separate the interseismic and coseismic movements. Additionally, a displacement field is derived from a denser GPS network of 30 stations. We model the coseismic movements by a dislocation in a homogenous elastic half space. The data do not allow to infer the fault strike direction, which have helped to understand the relationships with the regional geodynamics. However, the models give consistent figures for the fault surface (≈40 km2), the coseismic slip (1 m) and the depth of the upper and lower edges of the fault plane (2 and 6 km).
Interchange instability in the inner magnetosphere associated with geosynchronous particle flux decreases
Authors: Sazykin S. , Wolf R. A. , Spiro R. W. , Gombosi T. I. , De Zeeuw D. L. , Thomsen M. F.
Published: October 2002

We simulate the inner magnetosphere during the magnetic storm of September 25, 1998 using the Rice Convection Model with boundary fluxes estimated from geosynchronous data. Model results indicate development of an interchange‐like instability in the dusk‐to‐midnight sector, producing ripple structures in the plasma density, swirls in the subauroral ionospheric electric field pattern, and undulations near the equatorward edge of the diffuse aurora. We suggest that these disturbances might be observable whenever a strong main‐phase ring‐current injection is followed by a major, sustained decrease in the plasma energy density at geosynchronous orbit, a circumstance that will also produce rapid decay of the storm‐time ring current.
On the connection between winter anomalous precipitation in the Iberian Peninsula and North West Africa and the summer subtropical Atlantic sea surface temperature
Authors: Rodriguez‐Fonseca Belen , de Castro Manuel
Published: October 2002

Recent studies show that the state of the winter NAO is led by changes in the North Atlantic (NA) sea surface temperature(SST) with some months in advance. This finding encouraged us to analyze the possible predictability of the precipitation in the Iberian Peninsula and North West Africa (IPNA) regions, two of the most NAO affected areas. The results of a lag‐Singular Value Decomposition analysis with the precipitation and the SST anomalies, show a possible connection between the first mode of the anomalous IPNA winter precipitation and the previous summer SST anomalies over the North Atlantic (NA) basin. The use of a Monte Carlo test confirms the significance of the results. And moreover, this SST pattern tends to persist from the previous summer months in the subtropical NA. To show that this connection is robust, a crossvalidation analysis is performed using, as a predictor, the anomalous summer SST in the NA basin.
Global estimates of the wind‐induced energy flux to inertial motions in the surface mixed layer
Authors: Watanabe Michio , Hibiya Toshiyuki
Published: October 2002

It is believed that large‐scale oceanic thermohaline circulation is strongly influenced by small‐scale ocean mixing processes. In order to satisfy the large‐scale advective‐diffusive balance of the meridional overturning circulation, about 2.1 TW (1 TW = 1012 W) of power is required for the ocean mixing processes. This power is thought to be supplied by internal tides as well as wind stress fluctuations. Although the global energy flux from internal tides is estimated to be about 0.9 TW based on astronomical measurements, direct estimate of the global energy flux from wind stress fluctuations has not been made so far. In this study, using a simple numerical model, we estimate the wind‐induced global energy flux to inertial motions in the surface mixed layer. The calculated results show that the estimated global energy flux falls short of the required value.
Estimation of sea surface salinity in the Bay of Bengal using Outgoing Longwave Radiation
Authors: Murty V. S. N. , Subrahmanyam Bulusu , Sarma M. S. S. , Tilvi V. , Ramesh Babu V.
Published: October 2002

A new technique for retrieval of sea surface salinity (SSS) from space‐borne satellite measurements of Outgoing Longwave Radiation (OLR) through the ‘Effective Oceanic Layer (EOL)’ is explained in this paper. The OLR is used to study the convection over the land and ocean. This study is based on the idea that intense convection over the ocean is associated with warmer surface temperatures maintained by low surface salinities formed due to large riverine input and compounded by convection‐induced precipitation. This study augments the in situ SSS measurements. A preliminary assessment of deriving SSS from OLR is presented for the Bay of Bengal. It is envisaged that the SSS estimated in this way may be useful in improving the existing climatologies at least for those parts of the world's ocean where intense convection is the regular feature, such as the tropical Indian and Pacific Oceans.
Evidence for negative charging of the lunar surface in shadow
Authors: Halekas J. S. , Mitchell D. L. , Lin R. P. , Hood L. L. , Acuña M. H. , Binder A. B.
Published: October 2002

Observations of electron distributions above the shadowed surface of the Moon show energy‐dependent loss cones which indicate reflection by both magnetic and electric fields. At the same time, low energy (≲100 eV) field aligned upward‐going electron beams are observed. Together, these observations imply average night‐side potential differences between the surface and the Lunar Prospector (LP) spacecraft of ∼−35 V. The lunar surface may be at an even higher negative potential relative to the ambient plasma, since LP will likely also charge negative. The potential difference is consistent with simple current balance models which include secondary emission. No clear dependence is found on surface terrane type and age, or on ambient electron density and temperature. Instead, the potential difference is found to depend strongly on the angle from the subsolar point and the angle between the magnetic field and the normal to the lunar surface.
Association between quiet‐time Pi2 pulsations, poleward boundary intensifications, and plasma sheet particle fluxes
Authors: Sutcliffe P. R. , Lyons L. R.
Published: October 2002

Pi2 pulsations have been observed to occur at low latitudes during extremely quiet conditions. We have found an excellent correlation between an occurrence of such a Pi2 train and high‐latitude Pi2 pulsations and bay‐like disturbances in ground magnetic field of the type associated with poleward boundary intensifications (PBIs). The Pi2s and the PBIs that are inferred to occur simultaneously, show a ∼30 min repetition rate. They also exhibit an excellent correlation with energetic particle enhancements in the near Earth tail plasma sheet. These associations demonstrate the large‐scale nature of the magnetosphere‐ionosphere disturbance that gives rise to PBIs and shows that the disturbance may have important effects on energetic plasma sheet particles. They show for the first time that PBIs are associated with clearly observable Pi2 pulsations at low latitudes. Our observations are consistent with the possibility that PBIs are part of a large‐scale magnetospheric oscillation with ∼30 min period.
Climate responses to a doubling of atmospheric carbon dioxide for a climatically vulnerable region
Authors: Snyder Mark A. , Bell Jason L. , Sloan Lisa C. , Duffy Philip B. , Govindasamy Balasubramanian
Published: October 2002

Global modeling studies of future climate change predict large scale climatic responses to increased atmospheric carbon dioxide (CO2). While there have been several regional climate modeling studies that produced results at spatial and temporal scales relevant for climate change impact analysis, few have employed statistical significance testing of results. In a sensitivity study that focused on mean climate states, we use a regional climate model to generate ensembles of climate scenarios under atmospheric conditions of 280 and 560 ppm CO2, for a domain centered over California. We find statistically significant responses by mean annual and monthly temperature, precipitation, and snow to CO2 doubling. Relative to the 280 ppm results, 560 ppm results show temperature increasing everywhere in the region annually (up to 3.8°C), and in every month, with the greatest monthly surface warming at high elevations. Snow accumulation decreased everywhere, and precipitation increased in northern regions by up to 23%, on a mean annual basis.
Modeling geographic impacts on early Eocene ocean temperature
Authors: Najjar Raymond G. , Nong Giang T. , Seidov Dan , Peterson William H.
Published: October 2002

A general circulation model is used to evaluate the impact of geographic differences between the early Eocene and the present day on ocean thermal structure. The model includes reconstructed Eocene bathymetry and surface thermal boundary conditions that mimic a diffusive atmosphere. The model estimates that bathymetric changes alone caused surface waters to cool by 3–4°C in high latitudes and warm by 1–2°C in low latitudes over the last 55 million years, which would account for as much as half (∼4–5°C) of the increase in the meridional sea surface temperature gradient during this time. Other changes include a cooling (∼2°C) of deep ocean waters, a warming of low‐latitude intermediate waters (∼2°C), and decreases in Southern Ocean zonal sea surface temperature gradients.
Dimethylsulfide, a limited contributor to new particle formation in the clean marine boundary layer
Authors: Cainey Jill , Harvey Mike
Published: October 2002

Condensation sinks for sulfuric acid are predicted using measured aerosol number distributions for five sites, Baring Head and Cape Grim (clean marine), Tarawa (equatorial clean marine), the East Antarctic Plateau and the free troposphere (ultra clean). The condensation sink determined at each site allowed an estimate of the minimum level of sulfur dioxide required for new sulfate particle formation at that site. The sulfur dioxide concentration required for new particle production is nearly two orders of magnitude larger than the observed average at the sites assessed, except the free troposphere. In the marine boundary layer any available sulfur dioxide is converted heterogeneously to sulfate via the condensation sink. This implies that a significant proportion of the sub‐micron sulfate aerosol in the marine boundary layer is likely to have been entrained from the free troposphere, where a limited condensation sink and sufficiently high levels of sulfur species can support homogeneous nucleation.
Water vapour measurements inside cirrus clouds in Northern and Southern hemispheres during INCA
Authors: Ovarlez Joëlle , Gayet Jean‐François , Gierens Klaus , Ström Johan , Ovarlez Henri , Auriol Frédérique , Busen Reinhold , Schumann Ulrich
Published: October 2002

Water vapour data inside cirrus clouds from in‐situ measurements with an aircraft‐borne frost‐point hygrometer are analysed. These data have been obtained during two field campaigns, performed in the Southern and Northern hemisphere mid latitudes. There were many occurrences of ice supersaturation inside the investigated cirrus, with a higher frequency of occurrences in the Southern Hemisphere. The source of the differences in the humidity data from the two hemispheres is not clear, and it is speculated that these differences may be related to different levels of pollution. A distribution law for the relative humidity inside cirrus clouds is inferred.
Global structure of Bidecadal precipitation variability in boreal winter
Authors: Minobe Shoshiro , Nakanowatari Takuya
Published: October 2002

Three global monthly precipitation datasets, including gauge measurements, gauge/satellite merged analysis (CMAP), and NCEP/NCAR reanalysis, are analyzed with respect to Bi‐Decadal Oscillation (BDO) in boreal winter during the 20th century. Correlation and coherency analyses between the precipitations and the strength of the Aleutian low, which is an action center of the BDO, reveal substantial impacts of the BDO on precipitations around the Pacific Ocean. The covariability of the precipitations is prominent for Hawaii, mid‐latitude eastern North America, Florida and eastern‐China/Southern‐Japan, and at some other regions including the Southern Hemisphere. The most coherent BDO precipitation pattern common to the CMAP and reanalysis features significant anomalies over the tropical (10°–30°N), central (30°–50°N) and northern (50°–70°N) North Pacific with alternating polarities. The influence of the BDO on Hawaii winter droughts and salinity in the North Pacific is discussed.
On the importance of subsurface variability for ENSO simulation and prediction with intermediate coupled models of the Tropical Pacific: A case study for the 1997–1998 El Niño
Authors: Dewitte Boris , Gushchina Dacha , duPenhoat Yves , Lakeev Sergey
Published: October 2002

Two intermediate ocean‐atmosphere coupled models of the tropical Pacific are used to investigate the sensitivity of the forecasts of the 1997–1998 El Niño to the configuration of the oceanic vertical structure. The models consist in a three baroclinic mode tropical Pacific Ocean and differ from their atmospheric part which is either a Gill (1980)'s tropical atmosphere or a statistical atmosphere. Forced with observed winds, the ocean model simulates dynamical fields in better agreement with observations compared to a single baroclinic mode model. In forecasting sea surface temperature anomalies in the eastern Pacific, the models are comparable to prediction systems of similar complexity. Results of sensitivity tests to the oceanic vertical structure indicate that the second and third baroclinic mode contributions are necessary to better capture the rise in SST anomalies from April 1997 along with the amplitude of the event at its mature phase.
Pressure dependence of H solubility in magnesiowüstite up to 25 GPa: Implications for the storage of water in the Earth's lower mantle
Authors: Bolfan‐Casanova N. , Mackwell S. , Keppler H. , McCammon C. , Rubie D. C.
Published: October 2002

The solubility of hydrogen in (Mg0.93Fe0.07)O was studied from 5 to 25 GPa at 1200°C under oxidizing conditions, using FTIR spectroscopy on quenched single crystals. OH solubility increases with increasing pressure, concomitant with a decrease in ferric iron content. This result suggests that under lower mantle conditions, the charge neutrality condition could change from [FeMe·] = 2[V″Me] to [(OH)O·] = 2[V″Me], which would have important implications for the rheology of that region. The OH solubility data are well explained by incorporation of H as isolated hydroxyl groups via reduction of ferric iron. The amount of H incorporated at 25 GPa and 1200°C is ∼100 H/106 Me (Me = Mg, Fe), i.e. ∼20 ppm wt H2O, under water‐saturated conditions. When integrated over the entire mass of the lower mantle, these 20 ppm wt H2O amount to about 7.3 × 1018 kg H2O, a storage capacity of ∼0.5% of the ocean mass.
Genesis of mud volcanoes in sedimentary basins: A solitary wave‐based mechanism
Authors: Revil A.
Published: October 2002

Mud volcanoes represent the ground surface morphological expression of highly focused fluid flow inside sedimentary basins. Sedimentary basins show usually the presence of overpressured compartments encapsulated by low‐permeability bounds (seals), which can have different origins (capillary barriers with high entry capillary pressure, diagenetically sealed formations..). A mud volcano can be formed in response to the hydrofracturation of such a permeability barrier. When introducing the pressure dependence of permeability in poroelasticity, the theory predicts the upsurge of fluid pressure fronts after the hydrofracturation of the seal (initial shock). These fronts take the form of hydro‐mechanical non‐linear shock waves, which are solutions of a Bürgers‐type equation. These (solitary) waves are associated with an upsurge of pore water, which depends on the pore fluid pressure gradient carried up with the waves. The arrival of these waves at the ground surface can generate mud volcanoes‐type features with spots of highly focused flow.
Laboratory gouge friction: Seismic‐like slip weakening and secondary rate‐ and state‐effects
Authors: Chambon Guillaume , Schmittbuhl Jean , Corfdir Alain
Published: October 2002

We investigate experimentally the frictional response of a thick sample of simulated fault gouge submitted to very high shear displacements (up to 40 m) in an annular simple shear apparatus (ACSA). The frictional strength of our granular material exhibits velocity‐weakening consistent with classical rate‐ and state‐dependent friction laws. The length scale involved in the latter phenomenon is dc = 100 μm. However, the evolution of friction is largely dominated by a significant slip‐weakening active over decimetric distances (L = 0.5 m). Interestingly, these decimetric frictional length scales are quantitatively compatible with those estimated for natural faults. During shearing, a thin and highly‐sheared layer emerges from the thick and slowly‐deforming bulk of the sample. Because of the intermittent and non‐local coupling observed between these two zones, we relate the large frictional length scales in our data to the slow structuring of the thick interface.
By‐dependent prompt penetrating electric fields at the magnetic equator
Authors: Kelley Michael C. , Makela Jonathan J.
Published: October 2002

We propose a new type of prompt penetrating electric field effect which seems to be related to the y‐component of the interplanetary magnetic field and the NBZ current system. We report an equatorial electric field pattern which is not consistent with present understanding of prompt penetrating electric fields. The associated unbalanced excess NBZ current in one hemisphere partially flows across the nighttime equatorial zone. We find that a current system closes perpendicular to the ecliptic plane in the solar wind with a direction opposite to the interplanetary electric field. This is required for an MHD generator located in the solar wind.
Deep low‐frequency earthquakes beneath the focal region of the Mw 6.7 2000 Western Tottori earthquake
Authors: Ohmi Shiro , Obara Kazushige
Published: October 2002

On October 6, 2000, an Mw = 6.7 crustal earthquake occurred in western Tottori prefecture, southwest Japan. Beneath the focal region of the earthquake, deep low‐frequency (DLF) earthquakes were observed at depths of around 30 km. Five DLF earthquakes were detected within 3 years before the mainshock and more than 60 DLF earthquakes were observed during the 13 months after the mainshock. We investigated the focal mechanism of the DLF earthquake that occurred 9 hours before the mainshock, using amplitude ratios of the S‐waves to the P‐waves and polarization patterns of the S‐waves. Both analyses indicated that a single‐force source mechanism is more preferable than a double‐couple source mechanism, which suggests the transport of fluid such as water or magma. This event is probably another example of DLF earthquakes that occur beneath active fault zones.
The Sun at solar minimum: North ‐ south asymmetry of the polar coronal holes
Authors: Zhang J. , Woch J. , Solanki S. K. , von Steiger R.
Published: October 2002

Data from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses and synoptic charts derived from Kitt Peak magnetograms are used to compare the south and north polar coronal holes which existed during the declining/minimum phase of the solar activity cycle from 1992 to 1997. The kinetic properties of the solar wind emanating from the two polar coronal holes, as represented by solar wind speed, do not differ significantly. However, the electron temperature in the two coronal holes inferred from ionic charge composition data, namely the O7+/O6+ ratio, show consistent differences, with the south polar hole being 10 to 15% hotter. The ground‐based magnetograms show that the north polar coronal hole covers a larger part of the solar surface than the southern one. The total magnetic flux and, specifically, the flux density of the north polar coronal hole is considerably lower for the whole interval of time between 1992 and 1997. This strongly indicates that the difference in coronal hole temperature between the southern and northern coronal hole is intrinsic and is not due to the fact that the Ulysses observations in the south and north coronal hole streams were made at different phases of the solar cycle. Thus the differences found represent a real north‐south asymmetry during this time period.
Development of a strong shock in the outer heliosphere
Authors: Wang C. , Richardson J. D.
Published: October 2002

On October 16, 2001, Voyager 2 at ∼65 AU observed a strong shock with a speed jump of over 100 km s−1, the strongest shock observed since 1991. However, unlike for many large shocks observed in the outer heliosphere, we could not find a single solar event which is directly linked to this shock. Instead, a series of solar events in April 2001 is found to be responsible. A multi‐fluid one‐dimensional MHD model is used to show that the solar wind stream structures associated with the April solar events observed at Earth have merged in the distant heliosphere into the single strong interplanetary shock that was subsequently detected by Voyager 2 in October 2001. Our demonstration that large shocks can and do form from this merging mechanism may have important consequences for the formation of merged interaction regions and the triggering of the heliospheric radio emission.
Assessing ocean‐model sensitivity to wind forcing uncertainties
Authors: Burillo I. Andreu , Caniaux G. , Gavart M. , De Mey P. , Baraille R.
Published: October 2002

In this paper, we assess the short‐term forecast error of a mesoscale primitive‐equation open‐ocean model, induced by uncertainties in wind forcing. Statistics calculated from an ensemble of ocean states show that temperature forecast error is strongest at the top of the ensemble‐mean thermocline, as a consequence of vertical displacement of the mixed‐layer base around its ensemble mean. Horizontal pattern of the temperature error in the mixed‐layer is mainly explained by horizontal advection and surface heat flux fluctuations. These two mechanisms and entrainment through the mixed‐layer bottom are presented as the three processes responsible for thermal forecast error growth in the modeled upper ocean.
A comparison of mesospheric temperatures from the Canadian Middle Atmosphere Model and HALOE observations: Zonal mean and signature of the solar diurnal tide
Authors: Jonsson Andreas , de Grandpré Jean , McConnell John C.
Published: October 2002

Currently climate models are being extended to the middle atmosphere in order to investigate climate sensitivity in that region. This paper presents a comparison between the Canadian Middle Atmosphere Model (CMAM) climatology and 9 years of HALOE temperature measurements for the middle atmosphere. The analysis shows an overall agreement throughout the entire middle atmosphere with discrepancies within 10 K and less in various areas for both equinox and solstice conditions. For historical purposes, the analysis also includes a comparison with the CIRA‐86 reference model. In this case, the results indicate a significant CIRA‐86 warm anomaly in the upper mesosphere over the tropics which is particularly pronounced during equinox. Further analysis of the HALOE sunrise and sunset occultation measurements with the CMAM has revealed the signature of diurnal tides.
Analysis of seasonal cycles in climatic trends with application to satellite observations of sea ice extent
Authors: Vinnikov Konstantin Y. , Robock Alan , Cavalieri Donald J. , Parkinson Claire L.
Published: October 2002

We present a new technique to study the seasonal cycle of climatic trends in the expected value, variance, and other moments of the statistical distribution. The basis of the technique is multiple linear regression, but with periodic basis functions. The technique allows us to provide comprehensive information on statistical parameters of climate for every day of an observational period. Using daily data, the technique has no problems caused by different lengths of months or the leap‐year cycle. Without needing to assume the stationarity of contemporary climate, the technique allows the study of statistical parameters of climatic records of arbitrary length. We illustrate the technique with applications to trends in the satellite observed variations of sea ice extent in the Northern and Southern Hemispheres. We show that a significant part of the variability in hemispheric sea ice extents for the period 1978–1999 is related to linear trends.
General characteristics of temperature variation in China during the last two millennia
Authors: Yang Bao , Braeuning Achim , Johnson Kathleen R. , Yafeng Shi
Published: October 2002

Three alternate China‐wide temperature composites covering the last 2000 years were established by combining multiple paleoclimate proxy records obtained from ice cores, tree rings, lake sediments and historical documents. Five periods of temperature variation can be identified: a warm stage in AD 0–240, a cold interval between AD 240 and 800, a return to warm conditions from AD 800–1400, including the Medieval Warm Period between AD 800–1100, the cool Little Ice Age period between 1400–1920, and the present warm stage since 1920. Regional temperature variation is found during AD 800–1100, when warm conditions occurred in Eastern China and in the northeastern Tibetan Plateau and in AD 1150–1380, when the southern Tibetan Plateau experienced a warm interval. In contrast, evidence for cool conditions during the LIA is more consistent among the proxy records. The temperature reconstructions for China and the Northern Hemisphere show good agreement over the past millennium.
Evolution of subglacial bedforms along a paleo‐ice stream, Antarctic Peninsula continental shelf
Authors: Ó Cofaigh Colm , Pudsey Carol J. , Dowdeswell Julian A. , Morris Peter
Published: October 2002

Geophysical data from the Antarctic Peninsula continental shelf reveal streamlined subglacial bedforms in a cross‐shelf trough. Bedforms exhibit progressive elongation with distance along the trough, and record flow of a paleo‐ice stream from the Antarctic Peninsula Ice Sheet during the last glacial maximum. Downflow evolution of the bedforms indicates increasing flow velocities as the ice stream traversed the shelf. This, in turn, is related to a transition from crystalline bedrock on the inner shelf to a soft sedimentary substrate on the outer shelf. Although streaming flow operated across both substrates, the highest flow velocities occurred over the soft bed. Spatial variation in the inferred nature of fast‐flow, from sliding to subglacial sediment deformation and/or ploughing, was also lithologically controlled. These data highlight the control of subglacial geology on ice‐stream dynamics in the geological record and demonstrate a direct relationship between the formation of streamlined subglacial bedforms and paleo‐ice streams.
Nonlinear phenomena in fluids with temperature‐dependent viscosity: An hysteresis model for magma flow in conduits
Authors: Costa Antonio , Macedonio Giovanni
Published: October 2002

Magma viscosity is strongly temperature‐dependent. When hot magma flows in a conduit, heat is lost through the walls and the temperature decreases along the flow causing a viscosity increase. For particular values of the controlling parameters the steady‐flow regime in a conduit shows two stable solutions belonging either to the slow or to the fast branch. As a consequence, this system may show an hysteresis effect, and the transition between the two branches can occur quickly when the critical points are reached. In this paper we describe a model to study the relation between the pressure at the inlet and the volumetric magma flow rate in a conduit. We apply this model to explain an hysteric jump observed during the dome growth at Soufrière Hills volcano (Montserrat), and described by Melnik and Sparks [1999] using a different model.
The dependence of aerosol light‐scattering on RH over the Pacific Ocean
Authors: Hegg D. A. , Covert D. S. , Crahan K. , Jonssen H.
Published: October 2002

Measurements of the relative humidity dependence of aerosol light scattering are reported from three experimental venues over the Pacific Ocean. The measurement platform utilized was the CIRPAS Twin Otter aircraft. Results are compared with previous measurements at other locales and with theoretical models. The relatively low values of hygroscopicity obtained in marine air are consistent with a substantial organic component to the aerosol.