bluuebunny/crossref_metadata_2025 huggingface dataset:
Winter observations of the atmosphere over Antarctic sea ice
Authors: Kottmeier Christoph , Hartig Rüdiger
Published: February 2008

During the Winter Weddell Sea Project 1986 (WWSP 86), meteorological data were gathered above Antarctic sea ice in winter and spring. This paper discusses near‐surface data from 1986 and 1987, which were provided by weather stations deployed on drifting sea ice in October 1986. The drift tracks of these buoys for the subsequent 18 months document the sea ice motion of a larger fraction of the complete Weddell gyre than historical vessel drifts and previous buoy programs. The wind roses calculated from the buoys wind measurements show the large‐scale rotational wind field over the Weddell Sea. The northward components of near‐surface horizontal temperature gradients in winter vary between 1.3 and 2.6 K/100 km. Horizontal temperature gradients have a component toward the center of the gyre, which varies between 1 and 1.6 K/100 km in the central Weddell Sea. The marginal ice zone advances in autumn and retreats in spring with a speed significantly larger than the actual ice speed. Enhanced meridional temperature contrasts in the troposphere were found each time Polarstern passed the marginal ice zone. Significant mean horizontal temperature gradients of 1 to 5 K/100 km in the troposphere have also been detected in the continental marginal zone from Polarstern data and related aerological data of the Georg‐von‐Neumayer Antarctic station.
Ratio of leader to return stroke electric field change for first and subsequent lightning strokes
Authors: Rakov Vladimir A. , Uman Martin A. , Jordan Douglas M. , Priore Carmine A.
Published: February 2008

The ratio of leader to return stroke electric field change versus distance is presented as a function of stroke order for 218 first and subsequent strokes in 70 cloud‐to‐ground flashes which occurred near Tampa, Florida, in 1979. The measured leader to return stroke field ratio tended to be more negative as the stroke order increased, implying that the charge sources for successive strokes were, on average, progressively farther from both the observer and the ground strike point. Sixteen percent of all flashes analyzed contained at least one leader‐return stroke sequence with a negative net electric field change; that is, a ratio that is less than −1. These strokes were observed at distances from 2.5 to 11.6 km, with 56% farther than 8 km. They exhibited a strong tendency to occur late in a flash, with 89% occurring after the fourth stroke. The geometic mean initial electric field peak normalized to 100 km for strokes with a ratio less than −1 was found to be 1.1 V/m, 2.6 times lower than for all subsequent strokes in our data base.
Is recent climate change across the United States related to rising levels of anthropogenic greenhouse gases?
Authors: Plantico Marc S. , Karl Thomas R. , Kukla George , Gavin Joyce
Published: February 2008

Global warming as a result of rising concentrations of anthropogenic greenhouse gases is predicted by current climate models. During the period 1948–1987, the concentration of anthropogenic greenhouse gases increased by more than 30%, and the mean annual temperature of the northern hemisphere increased by about 0.15°C. The mean annual temperature of the contiguous United States, however, does not show any significant trend. To gain a better understanding of why the United States' temperature record does not reflect the anticipated greenhouse warming, we studied the inter‐relationships between trends of temperature, cloudiness, sunshine and precipitation. Both the seasonal and annual trends for 23 geographic regions covering the United States were analyzed using Monte Carlo field significance tests. Several seasonal and regional differences were noted. While winters and autumns cooled, springs and summers warmed. Annually, cooling has occurred across the eastern half of the country, while warming dominates in the West. The largest changes in maximum temperature, daily temperature range, cloud amount, percent of possible sunshine and precipitation occur during autumn. Autumn also has the most significant correlations between trends. We found that the recent decrease of the maximum temperature and daily temperature range in autumn is statistically associated with increasing cloud amount and precipitation, and with decreasing sunshine. The widespread reduction in the temperature range is a result of decreased maximum and increased minimum temperatures. Cloud amount increased over most of the country during all seasons except spring. During spring the cloud amount remained fairly constant even though precipitation increased. Interestingly, no significant correlation was found between trends of mean temperature and cloud amount. Although several features of the recent climate change across the United States agree qualitatively with the model‐predicted impact of increasing anthropogenic greenhouse gases, the regional and seasonal distribution of the observed trends do not appear in line with the model results. We conclude that either the recent changes of temperature, cloud amount, sunshine and precipitation over the United States are as yet unrelated to the increasing anthropogenic greenhouse gases, or that the transient response of regional climates to the greenhouse effect is not proportional to the modeled difference between the 1×CO2 and 2×CO2 equilibrium climates.
Airborne flux measurements and budget estimates of trace species over the Amazon Basin during the GTE/ABLE 2B expedition
Authors: Ritter John A. , Lenschow Donald H. , Barrick John D. W. , Gregory Gerald L. , Sachse Glen W. , Hill Gerald F. , Woerner Mary A.
Published: February 2008

In situ airborne measurements of turbulent heat, moisture, momentum, ozone, and carbon monoxide fluxes in a convective boundary layer were obtained over a tropical rain forest between 1100 and 1630 LT on May 4, 1987. The aircraft flight path was chosen so as to fly over the tower site at the Ducke Forest Reserve near Manaus, Amazonas, Brazil. Both turbulence statistics and mean quantities were used to study the budgets of heat, water vapor, ozone, and carbon monoxide. Residuals were found in the heat and water vapor budgets and are largely explainable in terms of the bandwidth of the respective sensors used for making flux measurements. The confidence of the findings for the O3 and CO budgets were found to be limited by the error in the determination of the along‐track advective component. The ozone budget study shows an accumulation rate in the boundary layer of 0.3±0.2 ppbv h−1. The surface resistance to ozone during this flight was determined to be 0.06±0.03 s cm−1, while the aerodynamic resistance was 0.14–0.17 s cm−1. Results from the CO budget analysis show a midday accumulation rate of 0.6±0.3 ppbv h−1 in the Amazonian boundary layer. The evidence suggests production of CO in the PBL. A source of CO may exist below the lowest flight level (≈ 150 m), although it was not possible to determine what part of the flux at flight level was due to chemical production and what part may be due to surface emission.
Seasonal variation of cloud radiative forcing derived from the Earth Radiation Budget Experiment
Authors: Harrison E. F. , Minnis P. , Barkstrom B. R. , Ramanathan V. , Cess R. D. , Gibson G. G.
Published: February 2008

The NASA Earth Radiation Budget Experiment (ERBE), flying aboard multiple satellites, is providing new insights into the climate system. Monthly averaged clear‐sky and cloudy sky flux data derived from the ERBE are used to assess the impact of clouds on the Earth's radiation balance. This impact is examined in terms of three quantities: longwave, shortwave, and net cloud forcing. Overall, clouds appear to cool the Earth‐atmosphere system. The global mean cooling varied from 14 to 21 W m−2 between April 1985 and January 1986. Hemispherically, the longwave and shortwave cloud forcing nearly cancel each other in the winter hemisphere, while in the summer the negative shortwave cloud forcing is significantly lower than the longwave cloud forcing, producing a strong cooling. Thus clouds significantly reduce the seasonal changes in the net radiative heating of the planet. This reduction is particularly strong over the mid‐ and high‐latitude oceans, where they reduce the summer and spring solar heating by as much as 100–150 W m−2. In the low latitudes, the longwave and shortwave cloud forcing reach peak values over the convectively disturbed regions and tend to offset each other to a large extent. This feature, when combined with the large cooling effect over mid‐ and high‐latitude oceans, leads to the conclusion that clouds significantly reduce the equator‐to‐pole radiative heating gradient of the planet during spring and summer. In the tropical convective regions the large magnitudes of the shortwave and longwave forcing and the near cancellation of the two suggest that clouds have a significant influence on the vertical distribution of heating between the atmosphere and the surface. Thus the ERBE data reveal that globally, hemispherically, and zonally, clouds have a significant effect on the radiative heating gradients. Comparisons of the ERBE results with general circulation models (GCMs) show that global net cloud forcing can be determined reasonably well from some current versions of the GCMs. Modeled regional and zonal values of radiative cloud forcing, however, indicate a need for considerable improvement.
Airborne sodium lidar measurements of gravity wave intrinsic parameters
Authors: Kwon Kang H. , Gardner Chester S.
Published: February 2008

We describe a data analysis technique for determining gravity wave intrinsic parameters including wave propagation direction. The technique involves measuring the altitude variations of the wave‐induced density perturbations of the atmospheric Na layer. This technique can be used with airborne lidars, multiple ground‐based lidars, and steerable lidars. In this paper the technique is applied to airborne Na lidar data obtained during a roundtrip flight from Denver, Colorado, to the Pacific Coast in November 1986. During the flight, strong wave perturbations were observed in the Na layer near the Pacific Coast over a horizontal distance of nearly 700 km. The intrinsic horizontal wavelength of this wave was estimated to be about 85 km, and the vertical wavelength was 4.1 km. The intrinsic period was about 102 min, and the propagation direction was almost due south.
Late Quaternary paleoceanography of the Tropical Atlantic, 1: Spatial variability of annual mean sea‐surface temperatures, 0‐20,000 years B.P.
Authors: Mix Alan C. , Ruddiman William F. , McIntyre Andrew
Published: February 2008

At least two modes of glacial‐interglacial climate change have existed within the tropical Atlantic Ocean during the last 20,000 years. The first mode (defined by cold glacial and warm interglacial conditions) occurred symmetrically north and south of the equator and dominated the eastern boundary currents and tropical upwelling areas. This pattern suggests that mode 1 is driven by a glacial modification of surface winds in both hemispheres. The second mode of oceanic climate change, defined by temperature extremes centered on the deglaciation, was hemispherically asymmetrical, with the northern tropical Atlantic relatively cold and the southern tropical Atlantic relatively warm during deglaciation. A likely cause for this pattern of variation is a reduction of the presently northward cross‐equatorial heat flux during deglaciation. No single mechanism accounts for all the data. Potential contributors to oceanic climate changes are linkage to high‐latitude climates, modification of monsoonal winds by ice sheet and/or insolation changes, atmospheric CO2 and greenhouse effects, indirect effects of glacial meltwater, and variations in thermohaline overturn of the oceans.
Anoxic events, productivity rhythms, and the orbital signature in a Mid‐Cretaceous deep‐sea sequence from central Italy
Authors: Herbert Timothy D. , Stallard R. F. , Fischer Alfred G.
Published: February 2008

Albian pelagic sediments from the Umbrian Apennines exhibit rhythmic bedding in outcrop. High temporal resolution (∼ 4‐kyr spacing) sampling of carbonate, Si, and Al along a 1.6‐m.y. interval of core demonstrates that changes in accumulation rate of calcareous and siliceous microorganisms were controlled by insolation cycles. Optical densitometry logging correlates variations of geochemical parameters to episodes of deep‐sea anoxia, indicated by numerous black, laminated zones (“black shales”). Harmonic analysis of data shows oscillations at three frequencies, which correspond closely in estimated duration and ratio to the modern eccentricity and precessional orbital cycles. As in Pleistocene marine sequences, the eccentricity (approximately 100 kyr) term dominates the sedimentary variance in the Umbrian cycles. Anoxic episodes occur in phase with a limestone‐marl repetition and reflect minima of the precessional (21 kyr) cycle. The covariance of carbonate and silica, with estimates of foraminiferal abundances, suggest that carbonate cycles are the result of changes in surface productivity of calcareous organisms rather than an effect of dissolution or diagenesis. Recognition of orbital cyclicity provides a tool for making quantitative estimates of these changes. Productivity during anoxic events was uniformly low (0.4– 0.5 g/cm2/kyr carbonate, 0– .05 g/cm2/kyr silica), but it rose to high levels during oxygenated periods (1– 2.5 g/cm2/kyr carbonate, 0.1– 0.3 g/cm2/kyr silica). Vertical overturning and organic carbon flux decreased during anoxic episodes, but decreased oxygenation of the deep water led to enhanced preservation of the organic matter delivered. The degree of paleoceanographic variability indicated by this study requires that accepted notions of climate stability and oceanic quiescence during nonglacial times be reassessed.
Late Quaternary calcareous nannofossil biostratigraphy and sedimentation patterns: Fram Strait, Arctica
Authors: Gard G.
Published: February 2008

Sediment cores from the Fram Strait are dated by means of calcareous nannofossil biostratigraphy and are shown to represent, at the most, the last 300 kyr (oxygen isotope stages 1–8). Differences in sedimentation rates are mainly controlled by the bottom topography and the intensity of ice‐rafted deposition. Sedimentation rates are normally in the order of a few centimeters per kiloyear in the central Fram Strait but increase to over 10 cm/kyr in cores located on the continental slope. The highest sediment accumulation rates occurred on the shelf (several tens of centimeters per kiloyear).
Abyssal circulation and benthic foraminiferal changes near the Paleocene/Eocene boundary
Authors: Miller Kenneth G. , Janecek Thomas R. , Katz Miriam E. , Keil David J.
Published: February 2008

A major change in Cenozoic deep‐sea benthic foraminifera occurred in the Atlantic, Indian, and Pacific oceans near the Paleocene/Eocene boundary. Benthic foraminiferal abundance changes began at about 61.5 Ma at Pacific Deep Sea Drilling Project (DSDP) Site 577. A major extinction event followed at 58–57 Ma (between Zones P6a and P6b), and a series of first appearances continued until circa 55.5 Ma (Zone P6c). These faunal changes occurred during a 6°C warming of Pacific bottom water and may indicate that the primary cause was changing temperature. Other potential causes of the faunal turnover include global changes in surface ocean productivity and changing bottom water source regions. Comparison of benthic and planktonic δ13C records requires no change in the ratio of oceanic phosphorous to carbon during the late Paleocene to early Eocene, which weakens the case for (but does not disprove) a change in surface ocean productivity at this time. Interbasinal comparisons of benthic foraminiferal δ13C records document that water with high δ13C values filled the Cape Basin during the late Paleocene and possibly the early Eocene (circa 61–57 Ma), but apparently did not extend into the western basins of the Atlantic. This pattern suggests a supply of Antarctic source water for the Cape Basin and possible tectonic isolation of the western Atlantic basins during at least part of the late Paleocene. Carbon isotope comparisons show that bottom water supply to the Cape Basin was reduced in the early Eocene. Eolian grain size data suggest that a decrease in zonal wind intensity occurred at the end of the Paleocene. These late Paleocene climatic changes (bottom water warming and decreased wind intensity) correspond with evidence for an important global tectonic reorganization and extensive subaerial volcanism, which may have contributed to climatic warming through increased supply of CO2.
Pacific pelagic phosphorus accumulation during the last 10 M.Y.
Authors: Moody Judith B. , Chaboudy Louis R. , Worsley Thomas R.
Published: February 2008

As a limiting nutrient to marine life, phosphorus (P) is an effective tracer of today's marine productivity. The distribution of P in marine sediments likewise tracks the history of marine productivity because of its relative insolubility in seawater. CaCO3, biogenic opal, terrigenous sediment, and total P have been measured in cores from nine Pacific sites (Deep Sea Drilling Project (DSDP) 65, 66, 310, 77, 62, 572, 463, 586, and GPC‐3) and one subantarctic (DSDP 266) site. These sites were specifically chosen to provide information on biota burial flux changes with time for sedimentary sinks that represent key oceanographic variables, i.e., rate of upwelling, water depth, and carbonate dissolution gradient. The accumulation rates of these components for the last 10 Ma were then calculated from determined core age versus depth plots, core bulk density, and porosity data. The accumulation of P weakly correlates with that of CaCO3, moderately with that of total sediment, and very strongly with carbonate‐free accumulation. Two prominent peaks for all components occur at 2–3 Ma and 5–6 Ma, and record the chemical loading of dissolved CaCO3, SiO2, and P from glacially emergent continental shelves. These results indicate that continental shelf phosphorites form during interglacially high sea levels and correspond to low deep‐sea P accumulation rates, whereas glacially lowered sea levels allow for shelf bypassing and greater deep‐sea P accumulation rates.
Upper Cenozoic history of the Labrador Sea, Baffin Bay, and the Arctic Ocean: A paleoclimatic and paleoceanographic summary
Authors: Aksu A. E. , Mudie P. J. , Macko S. A. , de Vernal A.
Published: February 2008

Foraminifera, palynomorphs, and stable isotopes in planktonic foraminifera have been studied in piston cores from the northern Labrador Sea, southern Baffin Bay, and the Alpha Ridge region of the central Arctic Ocean. Foraminifera in cores from the Labrador Sea and southern Baffin Bay show glacial‐interglacial δ18O values similar to those reported from the Norwegian and Greenland seas. In contrast to the eastern North Atlantic Ocean, however, peaks of Subarctic foraminifera and dinoflagellates in the western North Atlantic cores show that relatively warm Atlantic surface water continued to flow into the northern Labrador Sea during the early glaciation growth phases of isotopic stages 2, 4, 6, and 8. Boreal and Subarctic pollen suggest that warm Atlantic air flowed into the northern Labrador Sea and Baffin Bay during the ice sheet growth phases. The advection of warm air masses and the presence of open waters during the summer probably provided moisture for the growth of the Laurentide, Innuitian, and Greenland ice sheets. Isotopic and microfossil records in Arctic cores can also be tentatively correlated with major high latitude north Atlantic glacial‐interglacial events. Magnetostratigraphic, palynological and amino acid dating, however, shows that sedimentation on the Alpha Ridge has been very slow during the past 0.73 m.y.; therefore, events of less than 20,000 years duration cannot be clearly discerned. Interpretation of pre‐Pleistocene paleoenvironments is further limited by the sparseness of calcareous and siliceous microfossils.
The Cenozoic seawater 87Sr/86Sr curve: Data review and implications for correlation of marine strata
Authors: Koepnick R. B. , Denison R. E. , Dahl D. A.
Published: February 2008

The strontium isotopic ratio (87Sr/86Sr) in seawater changes slowly over geologic time. This variation is caused by changes in the relative contribution of Sr from various isotopically distinct sources within the crust. The most important of these are high‐ratio sialic rocks from continents and low‐ratio mafic volcanic and mafic intrusive rocks from continental margins and ocean basins. A plot of Sr isotope ratio versus age for Phanerozoic marine samples produces a curve exhibiting many episodes of increasing and decreasing values. This variation can be used as a basis for temporal correlation of marine carbonate, sulfate, and phosphate sediments. Temporal correlations can be made between high‐latitude and low‐latitude sequences, deepwater and shallow‐water sequences, and normal‐marine and restricted‐marine (hypersaline/hyposaline) sequences. Satisfactory biostratigraphic correlations between such sequences are often hampered by either the absence of age‐diagnostic fossils or by the provinciality of faunal and floral assemblages. Rapid change that took place in the 87Sr/86Sr of seawater during most of the Cenozoic makes this era particularly well suited for precise temporal correlation. The seawater curve for the Cenozoic is subdivided into three segments: Quaternary to mid‐Miocene, mid‐Miocene to late Eocene, and late Eocene to early Paleocene. The mid‐Miocene to late Eocene curve segment exhibits a particularly steep slope, making this a promising interval for high‐resolution stratigraphic correlation. Although current data generally support the present configuration of the seawater curve, some revision of the curve is probably required in the vicinity of the Oligocene‐Eocene boundary. Establishment of the general configuration of the seawater curve for the Cenozoic has promoted efforts to refine the curve on the basis of construction of detailed Sr isotope profiles within individual stratigraphic sequences. A Sr isotope profile at Deep Sea Drilling Project (DSDP) site 590B suggests a complex Neogene seawater curve characterized by minor slope changes in the Pliocene and Miocene. These slope changes are not specifically identified in the seawater curve constructed from multilocation data. On the basis of this more complex curve, and in the absence of diagenetic complications, the ultimate Neogene stratigraphic resolution is estimated to range from 0.1 to 2 million years. Both the verification and the general stratigraphic applicability of this more complex Neogene curve are largely dependent on the degree of preservation of the original seawater ratio in marine samples.
Tethyan carbonate carbon isotope stratigraphy across the Jurassic‐Cretaceous boundary: An indicator of decelerated global carbon cycling?
Authors: Weissert H. , Channell J. E. T.
Published: February 2008

The carbon isotope record in four pelagic carbonate sections from the Southern Alps (northern Italy) across the Jurassic‐Cretaceous boundary has been correlated to biostratigraphy and magnetostratigraphy. The carbon isotope curve from bulk carbonates shows a decrease from Kimmeridgian to Early Tithonian (CM24–CM22) values of δ13C=+2.07 (± 0.14)‰ to Late Tithonian and Berriasian (CM18–CM14) values of δ13C=+1.26 (± 0.16)‰. The change in the carbon isotope record coincides with changes in Tethyan calcite and silica accumulation rates, with a drop in the calcite compensation depth in the Atlantic and Tethys oceans and with changes in organic carbon burial along the Eurasian margin of the Tethys. Reduced surface water productivity due to diminished transfer rates of biolimiting elements into the Atlantic and Tethys oceans can explain these observations. The decreased transfer rates of elements such as silica or phosphorus from continents into the oceans resulted from drier climatic conditions and decreased water runoff on continents bordering the Tethys and Atlantic oceans. The proposed changes in Tithonian ‐ Berriasian ocean chemistry and paleoclimate suggest that variations in the global carbon cycle were coupled with changes in the global hydrological cycle and in associated material cycles.
Alkenone molecular stratigraphy in an oceanic environment affected by glacial freshwater events
Authors: Jasper John P. , Gagosian Robert B.
Published: February 2008

The sedimentary record of a ratio (UK37) of long chain (C37) unsaturated alkenones is a useful indicator of glacial‐interglacial climatic change in the Late Quaternary northern Gulf of Mexico where a planktonic foraminiferal δ18O‐CaCO3 record is complicated by meltwater and/or fluvial events (Williams and Kohl, 1986). Application of a laboratory temperature calibration of the UK37 ratio (Prahl and Wakeham, 1987) to a Pigmy Basin hydraulic piston core record (Deep Sea Drilling Project core 619) suggested that the minimum glacial surface mixed layer (SML) temperature was 8°±1°C colder than the Holocene high SML temperature of 25.6°±0.5°C. This predicted glacial‐interglacial temperature difference was significantly larger than the differences predicted by either the foraminiferal δ18O or foraminiferal assemblage temperature methods (0.8°‐2.0°C). This large difference may be caused by local Prymnesiophyte assemblage changes in response to climatically induced hydrographic changes. Interglacial periods may be dominated by pelagic Prymnesiophyte assemblages, while glacial periods may be dominated by neritic assemblages. A combined mechanism of both climatically varying Prymnesiophyte species assemblage and depth of alkenone biosynthesis may account for the large difference between the temperature methods.
Review of mode theory of radio propagation in terrestrial waveguides
Authors: Wait James R.
Published: February 2008

This paper is an expository review of the theory of guided waves that occur in the earth's atmosphere. We introduce the subject by treating the problem of radio propagation around the surface of an airless spherical earth. This leads readily to the classical solutions of van der Pol and Bremmer and the more recent work of Fock in the USSR. The influence of a troposphere with a smooth profile of refractive index is then considered. This analysis, which follows the recent work of Armand, confirms that a monotonically varying or smooth profile will not change the basic structure of the diffraction field. The modifications resulting from the presence of a tropospheric duct are developed by using a parabolic profile of refractive index in the manner suggested by Fock, Weinstein, and Belkina. It is shown that the dominant modes in this system have low attenuation. The second and major part of the paper is devoted to the theory of the mode propagation of VLF radio waves. Here the effective waveguide is the space formed by the earth's surface and the lower edge of the ionosphere. The mode solution is developed as a natural generalization of the classical airless‐earth theory. It is shown, for frequencies less than about 10 kc/s, that the field may be described in terms of flat‐earth modes analogous to those in a straight rectangular microwave guide. At higher frequencies, however, the earth curvature plays a major role and the character and excitation of the modes are changed drastically. Complications resulting from the anisotropy of the ionosphere are also considered. A critical discussion of the recent work on the subject is given.
A review of atomic abundances in chondrites and the origin of meteorites
Authors: Urey Harold C.
Published: February 2008

A review of the sources of analytical data for the chondritic meteorites is given, and the latest data, particularly for the minor elements, are tabulated. Though the composition of the chondrites is remarkably constant as compared with terrestrial rocks, important variations in the concentrations of certain major and minor constituents occur, which make it impossible to conclude that any one type of chondrite could have been produced from another by simple physical processes. This is true for the carbonaceous, enstatitic, and the high‐ and low‐iron‐group chondrites. The origin of these chondrites is discussed mostly with reference to the author’s suggestions about the origin of the solar system. Only very complicated processes can account for the detailed characteristics of these objects. The possibility that the carbonaceous chondrites and particularly Wiik's type 1 of this group are the primitive material from which the meteorites and planets originated is considered, and it is concluded that these objects as a group cannot be such material (a conclusion reached by the author some ten years ago). The case for the type 1 carbonaceous chondrites' being this material is better, but serious arguments against this conclusion can be advanced; it is concluded that even this material has undergone some extensive chemical processing.
Radar studies of the planets
Authors: Goldstein Richard M.
Published: February 2008

The great improvements in power and sensitivity of radar plus the development of more refined and elaborate data analyses have made it possible to obtain a variety of information about the planets. Measurements now include not only simple range by time delay; velocity by Doppler shift; and radar cross section by power returned; but also the roughness of the planetary surface and its variation from place to place through the shape of the reflected spectrum and the extent of double reflection of circularly polarized signals; the axis and rate of rotation of the planet by Doppler broadening, tracking of spectral features, and other techniques; and the mapping of the planet surface by range‐gated (i.e. location by coupling range and velocity) spectrums. The principal results obtained have been a greatly improved value of the astronomical unit; a period of rotation of Venus of about 250 ± 50 days retrograde; a surface variability and roughness of Venus comparable with that of the moon; a very smooth surface on Mars; a somewhat rougher surface on Mercury; the existence of one shiny spot 1000 or more miles wide on Jupiter; and negligible effects from planetary ionospheres and the interplanetary medium.
On dilatancy in relation to seismic sources
Authors: Frank F. C.
Published: February 2008

The theory of the Osborne Reynolds dilatancy phenomenon is developed, and it is shown to contain an intrinsic instability of the type needed to account for seismic faulting. This theory requires the presence of fluids in those parts of the earth's crust and upper mantle that show seismic activity, but it provides a mechanism for concentrating the fluids from a distance into those regions that ultimately fail catastrophically. It provides an explanation for the very wide range of ‘time constants’ observed to be associated with earthquakes.
The application of the discrete Fourier transform in the estimation of power spectra, coherence, and bispectra of geophysical data
Authors: Hinich M. J. , Clay C. S.
Published: February 2008

The computation of power spectra, cross spectra, coherence, and bispectra of various types of geophysical random processes is part of the established routine. Since it is routine, some of the standard procedures need to be examined rather carefully to be certain that the assumptions behind the procedures are applicable to the data on hand. The basic criteria for a particular method are its resolution bandwidth, its variance, and its bias. In this paper several basic power‐spectrum estimation procedures are reviewed and their statistical and mathematical properties are discussed. The direct use of the discrete Fourier transform for various spectrum calculations is discussed in detail, and its properties are compared with the standard procedure that uses the cosine transform of the estimated correlation function.
Solar wind interaction with the geomagnetic field
Authors: Parker E. N.
Published: February 2008

The interaction of the solar wind with the geomagnetic field is a complicated physical phenomenon. This paper attempts to point out the various major effects involved directly in the interaction and to assess the degree to which the effects are, and are not, understood at the present time. It is a collection of my own thoughts, opinions, and prejudices on the solar wind interaction. I am looking forward to new results to be reported at this symposium, which, I hope, will render much of this review obsolete.
Auroras and polar substorms: Observations and theory
Authors: Hultqvist Bengt
Published: February 2008

The results of observations of auroras and polar magnetic substorms are compared with magnetospheric models. In general, present qualitative or semi‐quantitative magnetospheric models describe fairly well the basic features of auroras and magnetic substorms, or they can probably be adapted to the observations by minor modifications. However, some observations cannot currently be easily interpreted in terms of the models. Of these, the existence of two daytime precipitation zones and some detailed features of the observed particle energy spectrum are among the most important. The stationary models cannot account for the high‐energy part of the auroral particle spectrum seen also in quiescent auroras. Some peaks in the observed spectrum also seem to pose problems. On the whole, the quantitative problems of entry and energization of the auroral particles are still unsolved.
Composition of the upper clouds of Venus
Authors: Rea Donald G.
Published: February 2008

Recent developments have shed new light on the composition of the upper Venus clouds. An analysis of the Mariner 5 occultation data has led to improved temperature and pressure profiles. When these are combined with transit data, it is concluded that there is an optically thin cloud layer with a top at 81‐km altitude where the temperature and pressure are, respectively, 175°K and 3 mb. The inclusion of temperatures derived from the near‐infrared CO2 bands leads to the postulate of a second cloud deck with a top at 61‐km altitude, where T = 260°K and P = 240 mb. Additional important constraints on cloud models are imposed by the measured abundances of HCl and H2O, by the polarization data, and by the reflection and emission spectra. It is concluded that the leading candidate for the uppermost clouds is liquid drops of HCl‐H2O, that there is no recommended candidate for the second cloud deck, and that H2O ice is at most a minor component of these cloud systems.
Inferring the interplanetary magnetic field by observing the polar geomagnetic field
Authors: Wilcox John M.
Published: February 2008

L. Svalgaard and S. M. Mansurov have shown that it is possible to infer the polarity of the interplanetary magnetic field quite reliably from observations of the diurnal variation of polar geomagnetic fields. The effect is most prominent in the vertical component of geomagnetic observatories near the geomagnetic poles during several hours near noon. The interplanetary magnetic field observed with spacecraft near the earth is very similar to the mean solar magnetic field (i.e., the sun observed as though it were a star); thus the fact that observations of the polar geomagnetic field have existed without interruption since 1926 at the Danish Meteorological Institute station at Godhavn, Greenland, means that in effect the inferred solar magnetic field during five sunspot cycles is available for analysis. The specific nature of the relation between the interplanetary field and the polar geomagnetic field should aid toward physical understanding of the interaction between the two fields. It has already been shown that it is the direction of the azimuthal (i.e., not the radial or north‐south) component of the interplanetary field that is significant in causing this effect.
Infrasound from convective storms: Examining the evidence
Authors: Georges T. M.
Published: February 2008

Two kinds of waves, infrasonic pressure fluctuations recorded on the ground and certain wavelike fluctuations in ionospheric phase height recorded by ground‐based radio sounders, have been independently associated with some severe convective storms. When we compare their phenomenologies, such a remarkable similarity emerges that it is hard to avoid the conclusion that both waves are different manifestations, in different parts of the acoustic spectrum, of the same emission mechanism. We tabulate the constraints each observation imposes on possible source models and estimate the average acoustic power required. A case study of one storm observed with both techniques reinforces the hypothesis of a common emission mechanism.
Lunar science: The Apollo Legacy
Authors: Burnett D. S.
Published: February 2008

A general review of lunar science is presented, utilizing two themes: a summary of fundamental problems relating to the composition, structure, and history of the moon and a discussion of some surprising, unanticipated results obtained from Apollo lunar science. (1) The moon has a crust of approximately 60‐km thickness, probably composed of feldspar‐rich rocks. Such rocks are exposed at the surface in the light‐colored lunar highlands. Many highlands rocks are complex impact breccias, perhaps produced by large basin‐forming impacts. Most highlands rocks have ages of ∼3.9 × 109 yr; the record of igneous activity at older times is obscured by the intense bombardment. The impact rate decreased sharply at 3.8–3.9 × 109 yr ago. The impact basins were filled by flows of Fe‐ and, locally, Ti‐rich volcanic rocks creating the dark mare regions and providing the strong visual color contrast of the moon, as viewed from earth. Crustal formation has produced enrichments in many elements, e.g., Ba, Sr, rare earths, and U, analogous to terrestrial crustal rocks. Compared with these elements, relatively volatile elements like Na, K, Rb, and Pb are highly depleted in the source regions for lunar surface rocks. These source regions were also separated from a metal phase, probably before being incorporated into the moon. The physical properties of the lunar mantle are compatible with mixtures of olvine and pyroxene, although Ca‐ and Al‐rich compositions cannot be ruled out. Deeper regions, below ∼1000 km, are probably partially molten. (2) Lunar rocks cooled in the presence of a magnetic field very much stronger than the one that exists today, owing either to dynamo action in an ancient molten core or to an external magnetization of the moon. Lunar soil properties cannot be explained strictly by broken‐up local rocks. Distant impacts throw in exotic material from other parts of the moon. About 1% of the soil appears to be of meteoritic origin. Vertical mixing by impacts is important; essentially all material sampled from lunar cores shows evidence of surface residence. The surface layers of lunar material exposed to space contain a chemical record of implanted solar material (rare gases, H) and constituents of a lunar atmosphere (40Ar, Pb). Large isotopic fractionation effects for O, Si, S, and K are present. Physical properties of the surface layers are dominated by radiation damage effects. Lunar rocks have impact craters (≤1 cm) produced by microgram‐sized interplanetary particles. The contemporary micrometeorite flux may be much higher than is indicated by the microcrater densities, indicating time variations in the flux. Particle track studies on the returned Surveyor camera filter first showed that the Fe nuclei were preferentially enhanced in solar flares.
Mineralogy, petrology, and geochemistry of the lunar samples
Authors: Warner Jeffrey
Published: February 2008

The years 1971–1974 mark the maturing of lunar mineralogy, petrology, and geochemistry into a full‐fledged science. During these years the prime objective of lunar sample investigation teams changed from general surveys of the nature of returned lunar material into problem‐oriented studies. Four general areas of interest that evolved during these years are (1) the geochemistry of the bulk moon, (2) the lunar regolith, (3) the lunar mare basins, and (4) the lunar highlands and crust. About 1000 scientists have been engaged in attempting to determine the origin and evolution of the moon. Although little new light has been shed on the ultimate problem of the origin of the moon, the following paragraphs show that the years 1971–1974 have greatly added to our understanding of the moon as an evolving planet.
Laser measurements of the lunar distance
Authors: Bender Peter L.
Published: February 2008

Since the start of 1971, two additional optical retroreflectors for laser distance measurements have been placed on the moon [Faller et al., 1971, 1972a; Faller, 1972; Chang et al., 1972]. The Apollo 11, 14, and 15 reflectors form a large triangle on the lunar surface with sides of 1250, 1100, and 970 km. Thus the angular motion of the moon about its center of mass can be determined very accurately and separated from other parts of the problem [Mulholland and Silverberg, 1972]. The Apollo 15 reflector was made 3 times larger in area than the other two in order to allow laser ranging for geophysical purposes with telescopes of smaller aperture [Faller et al., 1972b].
Magnetospheric physics: Magnetic fields
Authors: Russell C. T.
Published: February 2008

Progress in magnetospheric physics during the last quadrennium was not achieved through any one or a number of significant new discoveries or breakthroughs. Rather the advance was manifested more in gradual changes in the collective magnetospheric consciousness: the spreading acceptance that the magnetosphere is indeed ‘open,’ the increasing awareness of the key role of magnetospheric dynamics (substorms) in governing the various magnetospheric processes, a deeper appreciation of the role of electric fields and currents parallel to the magnetic field, the unfolding of the complexities of the earth's bow shock and associated phenomena, a strengthening attack on the merging process via theoretical and laboratory work, and the generation by several groups of magnetospheric magnetic field models based on observational data.

The quadrennium also appears to have marked the end of the exploratory phase of magnetospheric studies with the launching of spacecraft into the last unexplored reaches of the magnetosphere and the resultant discovery and investigation of the polar cusp, at the boundary between the closed and open field lines over the day side magnetosphere, and the plasma mantle, a boundary layer of flowing plasma in the high‐latitude magnetotail. New records for closest boundary positions were established during this period. Previously, the magnetopause had been observed at synchronous orbit on ATS 1. However, in March 1970, even the shock crossed synchronous orbit, and solar wind plasma was detected at synchronous orbit. Then in August 1972, Explorer 45 crossed the magnetopause at 5.2 RE. If it is assumed that the magnetopause and shock surface simply changed scale sizes, the ATS 5 observation of solar wind represents the greater magnetospheric distortion.
Planetary magnetospheres
Authors: Hill T. W. , Michel F. C.
Published: February 2008

The study of extraterrestrial planetary magnetospheres during the past 4 years has experienced a dramatic growth in the availability of observational data and a concomitant growth in the level of scientific interest comparable to the experience of the early 1960's in the study of earth's magnetosphere. Owing in large part to the success of space probes to our four nearest neighbor planets, the domain of magnetospheric physics has grown from the study of ‘the magnetosphere’ into the study of ‘planetary magnetospheres.’

It has now become possible to identify three rather different categories of planetary magnetospheres: (1) intrinsic slowly rotating magnetospheres, (2) intrinsic rapidly rotating magnetospheres, and (3) induced magnetospheres. By ‘intrinsic’ we mean that the planet possesses a sufficiently strong magnetic field to hold the solar wind off its surface; by ‘induced’ we mean that the planetary field exists mainly by virtue of the solar wind interaction with the planet. The distinction between ‘rapidly rotating’ and ‘slowly rotating’ is a quantitative one, indicating whether or not the structure and dynamics of the magnetosphere are influenced strongly by the rotational energy of the magnetospheric plasma. Thus although corotation in earth's magnetosphere is a well‐documented fact, this rotation is sufficiently slow that it can be safely ignored in most considerations of the overall dynamics of the magnetosphere, so that earth's magnetosphere is slowly rotating by the above definition.
Geomagnetic storms and substorms
Authors: Siscoe G. L.
Published: February 2008

This report is divided into two main parts corresponding roughly to observations and interpretations. The observation section is subdivided into papers concerned with the solar wind, geomagnetic tail, the magnetosphere, and the ionosphere and atmosphere. These regions are of course interdependent, and the boundaries between them are not sharp. However, most papers are clearly assignable to one of the three groups. The few that are not are assigned to the most appropriate one or are multiply referenced. Papers on subjects included in other reports in this series are mentioned here if they bear directly on storms and substorms. Papers on ionospheric storms and the storm response of the neutral atmosphere are included in the references.
Numerical models of the ocean circulation
Authors: Pond Stephen , Bryan Kirk
Published: February 2008

Numerical models of the large‐scale circulation of the oceans have developed into a useful tool for the interpretation of oceanographic data and the planning of new observational programs. Idealized numerical models with simplified geometry and physics have extended the analytic theory of the wind‐driven ocean circulation into the range in which inertial effects determine the solution. Recent numerical work has shown how stratification and baroclinic instability further modify a wind‐driven ocean circulation. Other results obtained by simplified numerical models include important predictions about the spectral properties of geostrophic turbulence in the ocean. Another class of numerical models has been developed which attempts to model the geometry and physics of the ocean circulation in a more detailed way, allowing a quantitative comparison with observations. Interesting results have been obtained for the Indian Ocean which simulate the seasonal variations of the Somali Current. Other Soviet and U.S. model studies using the observed density field as input show that pressure torques acting on bottom topography can be as large as the torques exerted by the wind acting at the surface. As yet, detailed simulations of the ocean circulation in a major ocean basin which include the effect of mesoscale eddies have not been undertaken.