bluuebunny/crossref_metadata_2025_split huggingface dataset:
Age determination of recent cave deposits using excess 210Pb ‐ A new technique
Authors: Baskaran M. , Iliffe Thomas M. 
Published: February 2008

Cave deposits have been widely used as proxy recorders in deciphering palaeoclimate during the last glacial/interglacial maxima (∼ 120 ka) [Harmon et al., 1975; Atkinson et al., 1978; Goede and Harmon, 1983; Ayliffe and Veeh, 1989]. Palaeoclimatic studies of cave deposits for the past 1–1000 yr time scale require a precise dating technique, that until now has been lacking. Due to the multiple sources of carbon in speleothems, 14C dates obtained for recently deposited calcite are highly variable and thus, 14C dating techniques are not suitable to obtain speleothem ages for the past 1–1000 years.Here, we show for the first time that speleothems contain high concentrations of excess 210Pb and that this 210Pb excess can be successfully employed to obtain growth rates of speleothems deposited during the last 100 years. Of two specimens analyzed, a tubular “soda straw” stalactite yielded a longitudinal growth rate of 1.1 mm/yr, while a normal icicle‐shaped stalactite had a lateral growth rate of 0.028 mm/yr. The mass growth rates of these two speleothems (149 and 78 mg/yr respectively) are comparable within a factor of two. Studies of fine‐scale variations in the isotopic composition of recent speleothems will help to corroborate the validity of palaeoclimate records obtained using longer lived isotopes and extending back into Pleistocene.
The ionosphere and airglow of Venus: Prospects for Pioneer Venus
Authors: Cravens T. E. , Nagy A. F. , Chen R. H. , Stewart A. I. 
Published: February 2008

In December of 1978, the Pioneer Venus Orbiter/Probe (PV) Missions will conduct a comprehensive investigation of the ionosphere of Venus. The purpose of this paper is to bring into focus our very limited current knowledge of the chemistry and physics of the Cytherean ionosphere in preparation for the major changes in this understanding that are undoubtedly going to occur as the result of the Pioneer Venus observations.We have performed theoretical calculations of the energetics of the Cytherean ionosphere and we conclude that the PV measurements will find elevated ion and electron temperatures, resulting primarily from energy fluxes associated in some manner with the solar wind, and acting directly on the ion gas. Ultraviolet dayglow intensities were also calculated and we anticipate that the PV will observe hundreds of kR’s of CO2 related emission features such as the CO Cameron bands. Nightside ionosphere calculations were also made assuming the precipitation of energetic electrons as an ionization source, in order to reproduce observed (Venera 9, 10; Mariner 10) nightside electron density profiles. The intensities of some of the resulting emission features are also calculated.
On the infrared radiative properties of CO2 ice clouds: Application to Mars
Authors: Hunt Garry E. 
Published: February 2008

We have investigated the effect on the observed 20 µm brightness temperatures measured by the IRTM instrument, of the presence of cloud layers of CO2 ice particles. The results show that such clouds have a profound effect, and a layer corresponding to visible thickness of ∼0.5, can create brightness temperatures of 120‐130K, even when the surface is at 150K. This suggests that these clouds may also contribute to the effect of brightness temperatures below the CO2 frost point, which have been observed over the southern winter polar region.This article contains supplementary material.
Discrimination of a chestnut‐oak forest unit for geologic mapping by means of a principal component enhancement of Landsat multispectral scanner data
Authors: Krohn M. Dennis , Milton N. M. , Segal Donald , England Anthony 
Published: February 2008

A principal component image enhancement has been effective in applying Landsat data to geologic mapping in a heavily forested area of eastern Virginia. A chestnut‐oak forest unit, which occurs on metavolcanic rocks and some metaclastic rocks in the western Piedmont and on highly weathered upland gravel deposits in the eastern Piedmont, can be discerned on a digitally enhanced Landsat winter image. The image enhancement procedure consists of a principal component transformation, a histogram normalization, and the inverse principal component transformation. The enhancement preserves the independence of the principal components, yet produces a more readily interpretable image than does a single principal component transformation.To determine how the chestnut‐oak forest unit was being enhanced, average Landsat multispectral scanner (MSS) values were extracted for four sample forest types and were calculated through the inverted principal component transformation. Slope and intercept values for the linear histogram normalization were chosen to keep the scale between the raw MSS bands and the inverted principal component (PC) bands constant. Plots of the inverted principal component data show that the most separation between forest types is in inverted PC band 5. The chestnut‐oak forest unit is characterized by a high value for inverted PC band 5 as opposed to a low value for inverted PC band 4. In contrast, raw MSS band 4 is greater than MSS band 5 for the four forest types sampled in the winter image. Such observations cannot be readily deduced from analysis of only the principal component rotation matrix. They may ultimately provide a means to map the distribution of chestnut‐oak forest from Landsat.
Outer‐rise earthquakes and seismic coupling
Authors: Christensen Douglas H. , Ruff Larry J. 
Published: February 2008

Outer‐rise earthquakes can be separated into two basic categories based on focal mechanism: compressional and tensional events reflecting compressional and tensional outer‐rise stress regimes. We propose a model that connects the stress regime in the outer‐rise to the behavior of large subduction earthquakes and explains the focal mechanisms and both the temporal and spatial occurrence of outer‐rise earthquakes.We find that compressional outer‐rise events tend to occur oceanward of seismic gaps in seismically coupled subduction zones, or equivalently just prior to large subduction zone earthquakes. The compressional stress regime is probably caused by slip in adjacent subduction zone segments. There are two modes of occurrence for tensional outer‐rise earthquakes depending on whether they occur in coupled or uncoupled subduction zones. In coupled subduction zones, tensional events tend to occur after large subduction events as tensional stress from slab pull is temporarily transmitted to the outer‐rise. In subduction zones that are inherently uncoupled, tensional events can occur at any time. Therefore, in uncoupled subduction zones the outer‐rise is always in tension, and only tensional outer‐rise events occur there; while in coupled subduction zones, the outer‐rise is in a compressional state prior to large subduction earthquakes and a tensional state afterwards due to the large displacements.
Magnetotelluric deep electrical sounding and resistivity
Authors: Bennett D. J. , Filloux J. H. 
Published: February 2008

Since the previous report to the IUGG in this field [Hermance, 1971], geoelectromagnetic induction studies have steadily increased in importance as a means of delineating tectonic structure in the upper few hundred kilometers of the earth. Such an advance is due especially to (1) the development of various computational techniques of modeling, (2) the accumulation of further data in tectonically interesting regions, (3) the increase in our knowledge of the relationships between the electrical conductivity of crustal and upper mantle materials and other parameters such as temperature, physical state, free water content, and seismic velocity, and (4) the ability to interpret many studies in terms of terrestrial conductivity structures which not only provide useful tectonic information not obtainable by other means but also are generally consistent with other relevant geological and geophysical data. Further stimulus has been provided by the availability of good electromagnetic sounding data for the moon obtained by the Apollo series of lunar landings.An outstanding problem remains the limited resolution of these studies as compared to seismology, for example. In consequence, average conductivity‐depth profiles of the upper few hundred kilometers still remain quite poorly determined for most of the earth, and a corresponding level of nonuniqueness is passed on to the models of two or three‐dimensional terrestrial conductivity structure.
The geology of Mars: A brief review of some recent results
Authors: Mutch T. A. , Head J. W. 
Published: February 2008

Most of what we know about the geology of Mars derives from the data of the Mariner 9 mission. This dramatically successful orbital reconnaissance of the planet continued for almost an entire year, from November of 1971 to October of 1972. Although many of the Mariner 9 data remain unanalyzed, the initial phase of intensive study is complete.An international colloquium on Mars was held in November 1973 in Pasadena, California, under the sponsorship of the American Geophysical Union, the American Astronomical Society, and the National Aeronautics and Space Administration. The objective of the colloquium was to synthesize Mariner results and to identify important problems for additional study. Most of the papers presented at the colloquium have since been published, particularly in Icarus [22(2, 3), 1974] and in the Journal of Geophysical Research [79(24, 26), 1974]. An attractive summary of Mariner 9 results has been prepared by Hartmann and Raper [1974].
F‐region dynamics
Authors: Mayr H. G. , Harris I. 
Published: February 2008

Problems of upper atmosphere dynamics represent a challenge that in itself attracts and deserves considerable attention. In a broader picture, dynamic processes are manifestations of energization processes that we seek to understand. An attempt is made here to report primarily on the U.S. research effort over the last 4 years that directly or indirectly relates to an understanding of upper atmosphere and F‐region dynamics.The upper atmosphere or thermosphere is referred to as the region above the mesopause (80—90 km) where the neutral gas temperature begins increasing with height to values as high as 2000°K. It harbors a relatively dense plasma population—the ionosphere—which, controlled by electric and magnetic fields, affects the energetics and dynamics of the neutral atmosphere. Through current loads, the ionospheric plasma distribution can also affect the electric fields across the magnetosphere which in turn penetrate into the lower atmosphere. The distribution of this plasma, is in turn influenced by atmospheric mass and energy transport. In the lower thermosphere, winds are a source for dynamo electric fields.
Introduction to the report on geodesy
Authors: Williams Owen W. 
Published: February 2008

The achievements of the U.S. geodetic community during the years 1974–1978 between the General Assemblies of the IUGG are summarized in this section. During this quadrennium, American geodesy dramatically moved from the era of primarily meeting the traditional needs of surveying and mapping into one of supporting a broad spectrum of geophysical and planetary disciplines. This movement was aided by modern technology epitomized by the increases in Doppler satellite observations, multifrequency distance measurements, lunar and satellite laser ranging, very long base line interferometry (VLBI), satellite altimetry measurements and inertial positioning.By far the most spectacular achievement in the field of geodesy during this period was the global sampling of sea surface topography with precision radar altimeters aboard the National Aeronautics and Space Administration (NASA) GEOS‐3 and Seasat‐1 satellites. The GEOS‐3 altimetry data set, acquired over a 3‐year period (1975–78), significantly improved our knowledge of the global gravity field of the earth, the oceanic geoid and the related mean gravity anomalies. Had the Seasat‐1 not failed after 3 months, an even more detailed knowledge of the oceanic geoid would be available today. Even with this early demise, Seasat‐1 in 3 months collected more altimetry data with greater accuracy than did GEOS‐3 in 3 years.
Convection
Authors: Boss Alan Paul 
Published: February 2008

Convective motions must be responsible for transporting essentially all the thermal energy from the interior of the earth to the surface layers of the planet. This thermal energy is derived from sources such as radioactive decay, cooling of the planet, and from the release of gravitational energy associated with growth and differentiation of the core. While the very presence of plate tectonics on earth is often considered prima facie evidence for at least upper mantle convection, the motion of the lithospheric plates on the surface of the earth also gives an indication of the patterns of convection in the underlying layers of the mantle.Convective motions are difficult to rigorously model in general because of the three dimensional, time dependent, multiple scale, nonlinear nature of the flows involved, and the complex rheology of the matter itself. Thus, while it is relatively easy to construct simplified models for how the Convective motions may be occurring on a global scale, or even detailed models of small‐scale phenomena, a rigorous, global model of the Convective processes in the earth's mantle and core, at the present time as well as throughout its evolution, consistent with the constraints imposed by geophysics, geochemistry, and dynamical modeling, does not exist. This deficiency is the fundamental problem that motivates much of the work on convection reviewed in this paper.
Precipitation analysis, modeling, and prediction in hydrology
Authors: Georgakakos Konstantine P. , Kavvas M. Levent 
Published: February 2008

In recent years U.S. meteorologists and hydrologists have shown increased interest in research related to modeling, observation and prediction (forecasting) of precipitation. In particular, mesoscale precipitation research has received most of the researchers' attention. This is mainly because of the following three reasons:1) There has been a shift of interest in the Atmospheric Sciences from the large scale to the mesoscale with emphasis in improving precipitation prediction (e.g., National Academies, Committee on Science, Engineering, and Public Policy, 1985; National Research Council, Ad Hoc Panel on Mesoscale Processes, 1981; National Research Council, Panel on Precipitation Processes, 1980; Court, 1979).
The French quadristatic incoherent scatter facility
Authors: Bauer P. , Waldteufel P. , Vialle C. 
Published: February 2008

The original Nançay‐St. Santin incoherent scatter facility based on the radio astronomy antenna at Nançay and a CW transmitter located at St. Santin (300 km south) was improved in many ways between 1965 and 1970: doubling of the transmitted power to 140 kw, lowering of the receiver noise level down to 100 K, monitoring of the antenna and data acquisition through the use of a computer, rejection of the parasitic tropospheric echoes.However, the most important improvement brought to the system is the addition of two new receiving stations 100 km east and west of the transmitter. Each of the new stations is equipped with a three‐beam Cassegrain antenna (25‐m parabola) aimed to simultaneously intersect the vertical transmitted beam at three different heights. Both new receivers have wide band (38 MHz at 3 db) gaseous helium cooled parametric amplifiers and on‐line computers. While one of the two new stations is equipped with filter banks for the purpose of spectral analysis, a different choice has been made for the other station. For the latter the data acquisition will imply multibit correlators, for both the ionic spectrum and plasma line measurements.Most of the improved electronic equipment designed for the new stations has also been implemented in the Nançay receiver. The frequency and time synchronization between the four sites is now accomplished by employing a single 5‐MHz frequency standard in each station monitored by standard time and frequency signals from MSF and/or HBG stations.The observation procedure consists of tilting the different receiving antennas so as to gather the signal scattered from the ionospheric vertical column illuminated by the transmitter. For calibration purposes a standard ionosonde is operating at St. Santin.The main objective of the quadristatic system is to determine completely the ion drift vector in order to study the electric fields and the neutral tidal winds. Other capabilities offered by the new system are a determination of the plasma line and a higher data acquisition rate.The first observations with one of the new stations were performed in December 1972.
Glossary of atmospheric electricity terms
Authors: Strong W. W. 
Published: February 2008

In this collection of terms used in connection with atmospheric electricity, especial attention is given to such which relate to ionization and radioactivity as it is in this direction that the greatest advances are being made.In designating the various products of any radioactive family of elements, the order of the products will be that of their formation. In all other cases, the order will be an alphabetical one.
The lunar‐diurnal magnetic variation and its relation to the solar‐diurnal variation
Authors: Egedal J. 
Published: February 2008

In an article published in this Journal the relation between the lunar‐diurnal and the solar‐diurnal variation has been discussed. The lunar‐diurnal variation being considered as generated by the solar‐diurnal variation under the influence of tidal forces, the following formula has been laid down: L/S f(ϕ) cos2ϕ = C (constant)In this formula L is the amplitude of the 12‐hour term of the harmonic formula for the lunar‐diurnal variation, S the daily oscillation of the magnetic element considered, and ϕ the geographical latitude of the place.
Effet de la distance de la lune sur l'amplitude diurne des éléments magnétiques
Authors: de Moidrey J. 
Published: February 2008

Cet effet, fort petit assurément, que nous avons signalé en 1916 (Terrestrial Magnetism, 1916, p. 25), avait besoin d'être confirmé et étendu. Comme il est douteux que nous puissions désormais publier notre travail, on nous permettra de donner le résultat.P et A désignent les amplitudes diurnes au périgée et à l'apogée, déterminées par 5 jours. Un contrôle par un seul jour donne même moyenne avec d'autres écarts moyens.
Some new theoretical and experimental results on the Aurora Polaris
Authors: Brüche Ernst 
Published: February 2008

A recent paper in Zeitschrift für Astrophysik reported on the new theoretical investigations1 undertaken by Prof. C. Störmer and also on experimental research carried out by the author on the theory of the aurora polaris.2The object of the theoretical investigation was to determine the periodic paths in space. The work dealt with types of paths which were hitherto unknown. The experimental research was confined to the practical production of electronic paths by employing models. The experimental results confirmed the theoretical work, and in addition, led to the determination of new paths.
The calculation of electrical resistivity for a region underlying two uniform layers
Authors: Roman Irwin 
Published: February 2008

In a previous paper,3 formulas and tables were obtained for computing the apparent electrical resistivity of a bed underlying a single uniform layer. Since the present paper may be considered as an extension of the previous paper, we shall omit all references except those specifically needed.There have been only a few papers on the present problem. Hummel4 has obtained a complete theoretical formulation for the simple case of a single overlying‐stratum. For the second approximation of two overlying‐strata, he has obtained formulas which can be interpreted most simply by anticipating the results of the present paper. The various potentials are expressible in double infinite series; for one counter, the general term is obtained; for the second counter, only the first four sets of terms are indicated; the law of formation for the general term is not given, except as just indicated; the results are given without derivation. The present results agree with those of Hummel, as far as his are given in explicit form. Stefanesco and Schlumberger5 solve the present problem in terms of Bessel functions and reduce their results to those of Hummel. Ehrenburg and Watson6 consider the problem of current‐flow through a medium composed of layers of equal thickness. The method is indicated for an arbitrary number of layers, but the explicit results are given only for those cases in which the upper layers are expressible without using more than five equally‐thick layers. The present results agree with those of these authors, as far as the two problems overlap, without extending their formulas. Both the Hummel and the Ehrenburg‐Watson papers seem to indicate a term‐by‐term calculation of the image‐strengths for positions accepted intuitively. There have been numerous other papers7 on the application of the electric resistivity‐method of prospecting, but few of them have any theoretical development, except on very broad approximations.
Occurrences of rapid micropulsations at Sodankylä during 1932 to 1935
Authors: Sucksdorff E. 
Published: February 2008

The rapid micropulsations, which are discussed herein, are shown in quick‐run records of terrestrial magnetism and earth‐currents as characteristic and easily distinguishable widenings of the curves, the shape of which is often reminiscent of that of a short shuttle. Single oscillations cannot be determined by the records, since the maximum period of an oscillation is less than 2 or 3 seconds—an interval not shown on the timescale of 180 mm per hour. Figure 1 gives reproductions of records, obtained February 6, 1935, of oscillations of this kind in magnetic declination and in both components of earth‐currents.Even a casual glance at the records reveals that rapid micropulsations occur in groups, and only from time to time. Usually they take place in the course of a few consecutive days, after which sometimes a week, or even a month, may pass before new oscillations occur. It is seldom that such an oscillation occurs singly; usually there is a number of oscillations, interrupted by short intervals, for one hour, for several hours, sometimes even for more than 24 hours continuously, when the curve often resembles a pearl necklace consisting of oval pearls of different sizes.