The Jovian surface condition and cooling rate

A theory which is almost fully analytic is used to investigate Jupiter's cooling rate. We find that a simple model of contraction with adiabatic interior structure gives a total cooling time to the present which is in good agreement with the age of the solar system. The interplay between the surface condition and the cooling rate is exhibited and discussed. The current rate of change of the effective temperature is calculated to be ?1°K/0.145×10⁹ yr. Discrepancies with fully numerical investigations of the Jovian age and cooling rate are noted.     

High spectral resolution ground-based observations of Venus in the 450- to 1250-cm−1 region

Ground-based observations of Venus were made with a 5-cm drive Michelson interferometer during December 1970 and December 1973. The thermal emission spectrum of the central portion of the apparent disk was recorded from 450–1250 cm^?1 with an apodized spectral resolution of 0.25 cm^?1. All statistically significant sharp line absorption features in the spectrum have been identified with gaseous CO₂. Comparison between the observed spectrum and a synthetic spectrum computed from a model atmosphere, assuming gaseous CO₂ and a sulfuric acid haze as opacity sources, indicates good agreement. A broad diffuse absorption feature associated with the sulfuric acid haze is evident in the 870- to 930 cm^?1 region. With the exception of the rotational lines of the 927-cm^?1 CO₂ band, the above feature appears as a continuum down to 0.25 cm^?1 resolution. In the 750- to 1250-cm^?1 range, the spectrum exhibits moderate thermal contrast with maximum brightness temperatures of 234–238°K occurring near 825 cm^?1. These temperatures are in general agreement with previous measurements.     

Infrared imaging of Jupiter in the 8–14-micrometer spectral region

High spatial resolution images of Jupiter were produced on the Hale 200-in. telescope in August 1974 and October 1975. A programmable wobbling secondary was used to raster scan the planet with 64 by 64 1-arsec pixels. Images were made with broadband (8–14 μm) and several 1- and 2-μm wide filters. All images reveal a belt and zone structure similar to visible pjotographs. Belts, in the broadband data, appear to be about 2°K hotter than the zones, but contrast varies markedly in different parts of the 8–14-μm spectral region. The lowest belt-zone contrast is found in the hydrogen opacity dominated region at 12.5 μm, while images at 9.5 μm exhibit the greatest contrast. Isolated areas are observed to be as much as 4°K hotter than surrounding areas at 9.5 μm. This large contrast is probably due to variations in the distribution of the ammonia clouds in the upper atmosphere.     

A model for inferring canopy and underlying soil temperatures from multi-directional measurements

Thermal emission is modeled from a canopy/soil surface, where the soil and the leaves are at different temperatures,T _g andT _c respectively. The temperatureT _m corresponding to a radiometer reading is given by $$B_\lambda (T_m ) = \chi B_\lambda (T_g ) + (1 - \chi )B_\lambda (T_c ) ,$$ whereB _λ denotes the Planck blackbody function at wavelength λ, χ specifies the fraction of the field of view occupied by the soil at a given view direction, and an emissivity of 1.0 is assumed for the plants and the soil. The dependence of the soil-fraction χ on the view direction and the structure is expressed by the viewing-geometry parameter, which allows for concise and simple formulation. We observe from our model that at large view zenith angles, only the plants are effectively seen (that is, χ tends to zero), and thereforeT _c can be determined from observations at large zenith angles, to the extent that such observations are practical. Viewing from the zenith, χ = exp(-L _hc), whereL _hc is the projection of the canopy leaf-area (per unit surface area) on a horizontal plane. For off-zenith observations, the soil-fraction χ depends on the distribution in the azimuth of the projected areas of various leaf categories, in addition to the dependence on the sum total of these projections,L _hc.L _hc, rather than the leaf-area index, emerges as the parameter characterizing the optical thickness of the canopy. Inferring bothT _c andT _g from observations from the zenith and from large zenith angles is possible ifL _hc is known from other measurements. Drooping of leaves under water-stress conditions affects the observed temperatureT _m in a complicated way because a leaf-inclination change produces a change inL _hc (for the same leaf area) and also a change in the dependence of χ on the view direction. Water stress can produce an increase of the soil-fraction χ and thus tends to produce an exaggerated increase in the observed temperature compared to the actual increase in canopy temperature. These effects are analyzed for a simulated soybean canopy.     

Stable isotope (O and C) and pollen trends in eastern Lake Erie,evidence for a locally-induced climatic reversal of Younger Dryas age in the Great Lakes basin

A cool period from about 11000 to 10 500 BP (11 to 10.5 ka) is recognized in pollen records from the southern Great Lakes area by the return of Picea and Abies dominance and by the persistence of herbs. The area of cooling appears centred on the Upper Great Lakes. A high-resolution record (ca. 9 mm/y) from a borehole in eastern Lake Erie reveals, in the same time interval, this pollen anomaly, isotope evidence of meltwater presence (a — 3 per mil shift in ¹⁸O and a +1.1 per mil shift in ¹³C), increased sand, and reduced detrital calcite content, all suggesting concurrent cooling of Lake Erie. The onset of cooling is mainly attributed to the effect of enhanced meltwater inflow on the relatively large upstream Main Lake Algonquin during the first eastward discharge of glacial Lake Agassiz. Termination of the cooling coincides with drainage of Lake Algonquin, and is attributed to loss of its cooling effectiveness associated with a substantial reduction in its surface area. It is hypothesized that the cold extra inflow effectively prolonged the seasonal presence of lake ice and the period of spring overturn in Lake Algonquin. The deep mixing would have greatly increased the thermal conductive capacity of this extensive lake, causing suppression of summer surface lakewater temperatures and reduction of onshore growing-degree days. Alternatively, a rapid flow of meltwater, buoyed on sediment-charged (denser) lakewater, may have kept the lake surface cold in summer. Other factors such as wind-shifted pollen deposition and possible effects from the Younger Dryas North Atlantic cooling could have contributed to the Great Lakes climatic reversal, but further studies are needed to resolve their relative significance.Contribution to Climo Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate ProgramGeological Survey of Canada Contribution 58 890     

Time resolved simulation of lightning by lip

In this letter, we report results of time resolved spectra of lightning simulation in air by laser-induced plasma (LIP). The measured electron temperatures varied from (1.7 +/- 0.1)X10(4) K at 600 ns to (1.2 +/- 0.1)X10(4)K at 4 microseconds after the ignition of the plasma. Electron densities in the plasma varied from (7.0 +/- 1.4)X10(17)/cm3 to (9.0 +/- 1.8)X10(16)/cm3 for the above times. We also present, for the first time, a comparison of state variables for LIP and natural lightning. We find that immediately following the ignition both natural lightning and LIP reach temperatures in excess of 16,000K and relax to ambient pressure with different rates. They are expected to approach 2000 - 4000 K temperature range, which is important to chemical synthesis, in an asymptotically similar fashion.     

Evidence for inherited Sm−Nd isotopes in granitoid zircons

This study presents evidence to show that, in addition to preserving U–Pb isotope systematics, refractory zircons also preserve, at least in part, an inherited Sm–Nd isotope component. The zircons analyzed during this study were taken from the Strontian granitoid (NW Scotland). The inner intrusion of this composite pluton is known from a previous study to contain substantial U–Pb zircon inheritance, whereas the outer part has only minor inheritance. Zircons from the inner intrusion were found to have significantly lower Nd₄₂₅ values than either their host rock, separated apatite or monazite. It is argued that this isotopic disequilibrium is due to the presence of an inherited Sm–Nd isotope component, rather than being due to a post-crystallization disturbance of the zircons. The preservation of inherted Sm–Nd isotopes within refractory zircons implies that they remain closed systems with respect to the diffusion of Sm and Nd (and presumably the other REE) to temperatures in excess of 700°C. The fact that zircons commonly have high Sm/Nd ratios, relative to sialic crustal material, means that the Nd isotopic evolution of inherited zircons will be very different to that of much of the continental crust.     

Amphibole composition in tonalite as a function of pressure: an experimental calibration of the Al-in-hornblende barometer

The Al-in-hornblende barometer, which correlates Al^tot content of magmatic hornblende linearly with crystallization pressure of intrusion (Hammarstrom and Zen 1986), has been calibrated experimentally under water-saturated conditions at pressures of 2.5–13 kbar and temperatures of 700–655°C. Equilibration of the assemblage hornlende-biotite-plagioclase-orthoclasequartz-sphene-Fe-Ti-oxide-melt-vapor from a natural tonalite 15–20° above its wet solidus results in hornblende compositions which can be fit by the equation: P(±0.6 kbar) = –3.01 + 4.76 Al _hbl ^tot r ²=0.99, where Al^tot is the total Al content of hornblende in atoms per formula unit (apfu). Al^tot increase with pressure can be ascribed mainly to a tschermak-exchange ( ) accompanied by minor plagioclase-substitution ( ). This experimental calibration agrees well with empirical field calibrations, wherein pressures are estimated by contact-aureole barometry, confirming that contact-aureole pressures and pressures calculated by the Al-in-hornblende barometer are essentially identical. This calibration is also consistent with the previous experimental calibration by Johnson and Rutherford (1989b) which was accomplished at higher temperatures, stabilizing the required buffer assemblage by use of mixed H₂O-CO₂ fluids. The latter calibration yields higher Al^tot content in hornblendes at corresponding pressures, this can be ascribed to increased edenite-exchange ( ) at elevated temperatures. The comparison of both experimental calibrations shows the important influence of the fluid composition, which affects the solidus temperature, on equilibration of hornblende in the buffering phase assemblage.