Are the high-latitude torsional oscillations of the sun real?

A numerical test is made to determine if the high-latitude torsional wave is generated from the low-latitude torsional pattern as a result of our reduction procedures. The results indicate that the high-latitude motions are not an artifact of the analysis, but are true solar features. We demonstrate also that the one-wave-per-hemisphere torsional oscillation does not result from the reduction procedure. These results place the observations in conflict with the predictions of - () models of the solar cycle.Now at Institute for Astronomy, University of Hawaii, Honolulu, Hawaii 96822, U.S.A.     

Solar limb brightening at the extreme limb from photoelectric eclipse observations

Photoelectric observations of the light intensity from the solar crescent before and after totality were made during the eclipses of 7 March, 1970 and 26 February, 1979. Effective wavelengths were determined by interference filters of 20 nm bandwidth. To obtain the limb darkening function, the resulting intensity curves were analyzed by an extension of the method of Julius in which we take into account the actual lunar limb profile. The limb darkening function at 433 nm was obtained for the region 0.937 < sin < 0.9999. Our results are in good agreement with existing center-to-limb measurements in the region of overlap which extends to sin = 0.99. Additional data were obtained at 600 nm for 0.994 < sin < 0.9999. The curves at both wavelengths show a distinctive limb brightening effect at sin = 0.999.     

Diploptene: an indicator of terrigenous organic carbon in Washington coastal sediments

The pentacyclic triterpene 17 beta(H),21 beta(H)-hop-22(29)-ene (diploptene) occurs in sediments throughout the Columbia River drainage basin and off the southern coast of Washington state in concentrations comparable to long-chain plantwax n-alkanes. The same relationship is evident for diploptene and long-chain n-alkanes in soils from the Willamette Valley. Microorganisms indigenous to soils and soil erosion are indicated as the biological source and physical process, respectively, for diploptene in coastal sediments. Similarity between the stable carbon isotopic composition (delta 13CPDB) of diploptene isolated from soil in the Willamette Valley (-31.2 +/- 0.3%) and from sediments deposited throughout the Washington coastal environment (-31.2 +/- 0.5%) supports this argument. Values of delta for diploptene in river sediments are variable and 8-17% lighter, indicating that an additional biological source such as methane-oxidizing bacteria makes a significant contribution to the diploptene record in river sediments. Selective biodegradation resulting from a difference in the physicochemical association within eroded particles can explain the absence of the more-13C-depleted form of diploptene in Washington coastal sediments, but this mechanism remains unproven.     

Fractionation of carbon isotopes by phytoplankton and estimates of ancient CO2 levels

Reports of the 13C content of marine particulate organic carbon are compiled and on the basis of GEOSECS data and temperatures, concentrations, and isotopic compositions of dissolved CO2 in the waters in which the related phytoplankton grew are estimated. In this way, the fractionation of carbon isotopes during photosynthetic fixation of CO2 is found to be significantly correlated with concentrations of dissolved CO2. Because ancient carbon isotopic fractionations have been determined from analyses of sedimentary porphyrins [Popp et al., 1989], the relationship between isotopic fractionation and concentrations of dissolved CO2 developed here can be employed to estimate concentrations of CO2 dissolved in ancient oceans and, in turn, partial pressures of CO2 in ancient atmospheres. The calculations take into account the temperature dependence of chemical and isotopic equilibria in the dissolved-inorganic-carbon system and of air-sea equilibria. Paleoenvironmental temperatures for each sample are estimated from reconstructions of paleogeography, latitudinal temperature gradients, and secular changes in low-latitude sea surface temperature. It is estimated that atmospheric partial pressures of CO2 were over 1000 micro atm 160 - 100 Ma ago, then declined to values near 300 micro atm during the next 100 Ma. Analysis of a high-resolution record of carbon isotopic fractionation at the Cenomanian-Turonian boundary suggests that the partial pressure of CO2 in the atmosphere was drawn down from values near 840 micro atm to values near 700 micro atm during the anoxic event.     

Sunspot group areas and the latitude distance from the average latitude of activity

Digitized Mount Wilson sunspot data from 1917 to 1985 are analyzed to examine group areas as a function of latitude distance () from the central latitude of activity in each hemisphere. On average these group areas are larger for the smallest values of ¦¦. The effect is similar to that seen for the magnetic fields of active regions (Howard, 1991). It is concluded that this is fundamentally a dependence, and not a latitude dependence. The suggestion is made that the cause of this effect is the influence of large-scale convective motions on the rising flux tubes that make up the active regions. The smaller flux tubes (spot groups) are more easily displaced in latitude during their ascent to the surface by this velocity field than are the larger flux tubes.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation.     

An estimate of the temperature and abundance of CH4 and other molecules in the atmosphere of Uranus

We present a preliminary analysis of CH₄ absorptions near 6800 Å in new high resolution spectra of Uranus. A curve of growth analysis of the data yields a rotational temperature near 100 K and a CH₄/H₂ ratio that is 1 to 3 times that expected for a solar type composition. The long pathlengths of CH₄, apparently demanded by absorptions near 4700 Å, are qualitatively shown to be the result of line formation in a deep, predominantly Rayleigh scattering atmosphere in which continuum absorption is a strong function of wavelength. The analysis of the CH₄ also yields a minimum value for the effective pressure of line formation (～ 2 atm). This value is shown to be twice that expected on Uranus if the atmosphere were predominantly H₂. It is speculated that large amounts of some otherwise optically inert gas is present in the Uranus atmosphere. N₂ is suggested as a possible candidate since there are cosmogonic reasons why Uranus should contain large amounts of N relative to C, He, and H, and also because the pressure-induced pure rotation spectrum of N₂ could possibly account for the low brightness temperatures that have recently been observed at 33 and 350 μm. If N₂ is present the planet probably possesses a surface at the 10–100 atmosphere level.     

Fluvial sediment transport and deposition following the 1991 eruption of Mount Pinatubo

The 1991 eruption of Mount Pinatubo generated extreme sediment yields from watersheds heavily impacted by pyroclastic flows. Bedload sampling in the Pasig–Potrero River, one of the most heavily impacted rivers, revealed negligible critical shear stress and very high transport rates that reflected an essentially unlimited sediment supply and the enhanced mobility of particles moving over a smooth, fine-grained bed. Dimensionless bedload transport rates in the Pasig–Potrero River differed substantially from those previously reported for rivers in temperate regions for the same dimensionless shear stress, but were similar to rates identified in rivers on other volcanoes and ephemeral streams in arid environments. The similarity between volcanically disturbed and arid rivers appears to arise from the lack of an armored bed surface due to very high relative sediment supply; in arid rivers, this is attributed to a flashy hydrograph, whereas volcanically disturbed rivers lack armoring due to sustained high rates of sediment delivery. This work suggests that the increases in sediment supply accompanying massive disturbance induce morphologic and hydrologic changes that temporarily enhance transport efficiency until the watershed recovers and sediment supply is reduced.     

Attenuation relations of ground motion for rock and soil sites in eastern United States

This paper presents the attenuation relations of peak ground acceleration and spectral accelerations for rock and soil sites in the central and eastern United States (CEUS). For the bedrock site condition, 56 pairs of moment magnitude M and epicentral distance R are used to simulate ground motion, and for each pair of M and R, 550 samples of ground motion parameters are generated using a seismological model together with random vibration theory and distribution of extreme values. From the regression analyses of these data, the attenuation relations of ground motion parameters for the bedrock site are established. With the aid of appropriate site coefficients, these attenuation relations are modified for the site categories specified in the 1994 NEHRP Provisions. These attenuation relations are appropriate for the assessment of seismic hazards at far-field rock and soil sites in the CEUS.     

Isotopic order, biogeochemical processes, and earth history: Goldschmidt lecture, Davos, Switzerland, August 2002

The impetus to interpret carbon isotopic signals comes from an understanding of isotopic fractionations imposed by living organisms. That understanding rests in turn on studies of enzymatic isotope effects, on fruitful concepts of isotopic order, and on studies of the distribution of ¹³C both between and within biosynthetic products. In sum, these studies have shown that the isotopic compositions of biological products are governed by reaction kinetics and by pathways of carbon flow.Isotopic compositions of individual compounds can indicate specific processes or environments. Examples include biomarkers which record the isotopic compositions of primary products in aquatic communities, which indicate that certain bacteria have used methane as a carbon source, and which show that some portions of marine photic zones have been anaerobic. In such studies, the combination of structural and isotopic lines of evidence reveals relationships between compounds and leads to process-related thinking. These are large steps. Reconstruction of the sources and histories of molecular fossils redeems much of the early promise of organic geochemistry by resolving and clarifying paleoenviron-mental signals. In turn, contemplation of this new information is driving geochemists to study microbial ecology and evolution, oceanography, and sedimentology.