Water, ammonia, and H2S mixing ratios in Jupiter's five-micron hot spots: A dynamical model

The Galileo probe entered the jovian atmosphere at the southern edge of a 5-micron hot spot, one of typically 8-10 quasi-evenly-spaced longitudinal areas of anomalously high 5-micron IR emission that reside in a narrow latitude band centered on +7.5 degrees. These hot spots are characterized primarily by a low abundance of the cloud particles that dominate the 5-micron opacity at other locations on the planet, and by significant desiccation of ammonia, water and hydrogen sulfide in the upper layers of the troposphere. Ortiz et al. [1998. Evolution and persistence of 5-micron hot spots at the Galileo probe entry latitude. J. Geophys. Res. 103, 23,051-23,069] found that the latitude and drift rate of the hot spots could be explained if they are formed by an equatorially trapped Rossby wave of meridional degree 1 moving with a phase speed between 99 and 103 m s⁻¹ relative to System III. Here we model additional properties of the hot spots in terms of the amplitude saturation of such a wave propagating in the weakly stratified deep troposphere. We identify the hot spots with locations where the wave plus mean thermal stratification becomes marginally stable. In these locations, potential temperature isotherms stretch downward to very deep levels in the troposphere. Since fluid parcels follow these isotherms under adiabatic flow conditions, the parcels dive downward when they enter the portion of the wave associated with the hot spot and soar upward upon leaving the spot. We show that this model can account for the anomalous vertical profiles of NH₃, H₂O, and H₂S mixing ratio measured by the Galileo probe. Pressures vary by as much as 20 bar over potential temperature isotherms in solutions that produce sufficient desiccation of water and H₂S in hot spots. Approximately 6×¹⁰⁻² of Jupiter's internal heat flux must be tapped to maintain the wave over the mean hot spot lifetime of 10⁷ s. The results suggest that the phenomenon that causes hot spots may occur widely, although in less dramatic form, across Jupiter's surface, and consequently NH₃, H₂S, and H₂O mixing ratio profiles may vary significantly from location to location in Jupiter's troposphere.     

Radiating dike swarms on Venus: evidence for emplacement at zones of neutral buoyancy

Theoretical calculations of extrusive volcanic degassing on Venus yield atmospheric pressure-related rock density profiles consistent with the formation of magma neutral buoyancy zones and magma reservoirs at different depths as a function of altitude (Head and Wilson, J. geophys. Res. 97, 3877, 1992). Global analysis of radiating dike swarms interpreted to originate at magma reservoirs show that their distribution matches these predictions across approximately 90% of the planet's surface; only those highland regions whose elevations exceed 6053 km appear anomalous. The distribution of the large volcano population (extrusive reservoir products) (Keddie and Head, Planet. Space Sci. 42, 455, 1994) has yielded similar results. Comparison between the dike swarm (intrusive) and large volcano (extrusive) populations suggests that neutral buoyancy plays an important role in governing volcanic processes near the venusian surface and that the depth to the level of neutral buoyancy increases systematically at altitudes above 6051 km.     

The dependence of the climate sensitivity on convective parametrization: statistical evaluation

Two sensitivity experiments, in which CO₂ is instantaneously doubled, have been performed with a general circulation model to determine the influence of the convective parametrization on simulated climate change. We have examined the spatial structure of changes in the annual mean and annual cycle for surface temperature and precipitation for both experiments; similarly we have examined changes in the variance for these two fields. We have also computed a range of test statistics in order to obtain reliable measures of the signal-to-noise ratio in the climate change signal from each experiment. We have computed test statistics for the entire globe and for five different region and we contrast the global response with the response in the Australian region taken as a representative sample.We find that the highest signal-to-noise ratios in the change from 1 * CO₂ to 2 * CO₂ are for the change in surface temperature for both experiments with little difference in the global averages between the experiments. Globally averaged precipitation shows a greater noise level but perhaps the greatest contrast between experiments. There are generally significant increases in the temporal and spatial variability of precipitation in the change from the 1 * CO₂ to 2 * CO₂ and with some differences apparent between the two experiments. The temporal variability of surface temperature does not change significantly in any of the 2 * CO₂ cases, and there is little difference between the experiments. There is a significant decrease in the spatial variability of surface temperature in all 2 * CO₂ experiments in all cases and with significant differences in the seasonal variations between different experiments. The spatial variability of precipitation increases in all 2 * CO₂ cases and also with substantial differences in the seasonal variations between the experiments. There are accompanying significantly different spatial pattern correlations for both surface temperature and precipitation. In general we find that the global changes are fairly robust with the differences associated with convective parametrization schemes being very small. However, at the regional level, there are marked differences between experiments with changes both in the means and in the spatial and temporal variances but often with low levels of significance.     

Dust-penetrated arm classes: insights from rising and falling rotation curves

In the last decade, near-infrared imaging has highlighted the decoupling of gaseous and old stellar discs: the morphologies of optical (Population I) tracers compared to the old stellar disc morphology, can be radically different. Galaxies which appear multi-armed and even flocculent in the optical may show significant grand-design spirals in the near-infrared. Furthermore, the optically determined Hubble classification scheme does not provide a sound way of classifying dust-penetrated stellar discs: spiral arm pitch angles (when measured in the near-infrared) do not correlate with Hubble type. The dust-penetrated classification scheme of Block & Puerari provides an alternative classification based on near-infrared morphology, which is thus more closely linked to the dominant stellar mass component. Here we present near-infrared K -band images of 14 galaxies, on which we have performed a Fourier analysis of the spiral structure in order to determine their near-infrared pitch angles and dust-penetrated arm classes. We have also used the rotation curve data of Mathewson et al. to calculate the rates of shear in the stellar discs of these galaxies. We find a correlation between near-infrared pitch angle and rate of shear: galaxies with wide open arms (the γ class) are found to have rising rotation curves, while those with falling rotation curves belong to the tightly wound α bin. The major determinant of near-infrared spiral arm pitch angle is the distribution of matter within the galaxy concerned. The correlation reported in this study provides the physical basis underpinning spiral arm classes in the dust-penetrated regime and underscores earlier spectroscopic findings by Burstein and Rubin that Hubble type and mass distributions are unrelated.     

Chemical studies of copper-organic complexes isolated from estuarine waters using C18 reverse-phase liquid chromatography

Dissolved organic matter (DOM) and dissolved copper-organic complexes were isolated from the estuarine waters of Narragansett Bay, RI, using reverse-phase liquid chromatography employing C₁₈ Sep-Pak cartridges (Waters Associates). The cartridges were found to have a constant retention efficiency for processing ? 1-l volumes of seawater. Fractionation of the isolated material, by sequential elution of the Sep-Pak with water: methanol mixtures of increasing organic solvent concentration, yielded a fraction of the organic matter with a specific copper activity six times greater than the overall activity for the isolated DOM. Analysis of this fraction by high performance liquid chromatography suggested that the organic components are of intermediate polarity and have appreciable aromatic character.An investigation of the protonation characteristics of the isolated complexes indicated that most of the copper is associated with a broad range of acidic sites on the DOM. Analysis by electron paramagnetic resonance spectroscopy confirmed the organic association of the isolated copper and also suggested the presence of several types of binding sites which probably involve oxygen donor ligands.Studies of the exchange of ⁶⁴Cu with these binding sites on the isolated DOM indicated that 70% of the sites undergo rapid exchange with copper in seawater while 20% of these sites did not exchange in a 24-h time period.     

Isolation of dissolved organic matter and copper-organic complexes from estuarine waters using reverse-phase liquid chromatography

Reverse-phase liquid chromatography was used for the isolation of dissolved organic matter and dissolved copper-organic complexes from the estuarine waters of Narragansett Bay, Rhode Island. The procedure isolates 10–30% of the organic matter and up to 50% of the total dissolved copper from various bay samples. Chromatograms obtained by high-performance liquid chromatography of the isolated organic matter showed qualitative differences between sampling stations progressing from the Providence River in the upper bay to the lower bay.     

Altered basaltic glass: A terrestrial analog to the soil of Mars

Analyses of Martian surface soil by Viking and Earth-based telescopes have been interpreted as indicating a regolith dominated by the weathering products of mafic or ultramafic rocks. Basaltic glass has previously been proposed as a more likely precursor than crystalline rock, given the low efficiency of surface weathering under present Martian conditions. On Earth large volumes of basaltic glass formed by quenching of magma by water. A similar interaction, between magma and ground ice, may have been a common occurrence on Mars. On the basis of this scenario palagonite, the alteration product of basaltic sideromelane glass, was studied as a possible analog to Martian soil. Samples from Iceland, Alaska, Antarctica, Hawaii, and the desert of New Mexico and Mexico were examined by optical and scanning electron microscopy, electron microprobe analysis, X-ray diffraction, spectrophotometry, and magnetic and thermogravimetric analysis. We suggest that palagonite is a good analog to the surface soil of Mars in chemical composition, particle size, spectral signature, and magnetic properties. Our model for the formation of fine-grained Martian surface soil begins with eruptions of basaltic magma through ground ice, forming deposits of glassy tuff. Individual glass shards are then altered by low-temperature hydrothermal systems to palagonitic material. Dehydration and aeolian abrasion strip the alteration rinds from the glass, and wind storms distribute the silt-sized palagonitic fragments in a planet-wide deposit.     

Vorticity waves in a shallow basin

Observed oscillatory current patterns in the southern basin of Lake Michigan, with a distinctive peak in the energy spectrum at a period of about 90 h, are simulated using a linear potential vorticity conservation model. Solutions of the forced vorticity equation in a paraboloidal basin show rotational, oscillatory motions tuned to the low-frequency topographic modes that are very similar to the observed flow patterns. Topography-controlled vorticity waves are excited most effectively by wind episodes with frequency nearly in resonance with the topographic modes. Bottom resistance has no significant effect on the frequency equation; it simply decays the waves slowly in the open lake and more quickly near the coast. Flow patterns of both the gravest free vorticity wave and the corresponding forced wave consist of two opposite circulation cells separated by a null streamline through the center of the basin and rotating cyclonically near the free wave and atmospheric forcing frequencies, respectively. Interactions between the forced and free waves result in an apparent rotational pattern with a frequency the median of the two. A combination of elliptic—paraboloidal basin and shorter period forced modes can approximate the observed Lake Michigan response. Doppler shift, due to the persistence of cyclonic vorticity in the flow field, is also determined to be a factor in shifting the elliptical basin mode to a higher frequency.     

A paleomagnetic study of the Mull lava succession

Summary. A paleomagnetic study has been made of a succession of 139 non-overlapping basaltic lavas, representing 91 per cent of the longest remaining succession of flows associated with the Paleogene Mull volcano. All the lavas have experienced considerable hydrothermal alteration, probably at up to several million years after initial magnetization and frequently with alteration to the opaque minerals and the production of new potentially magnetic phases. The question of whether directional remagnetization has taken place while preserving within-unit directional consistency and discreteness of unit mean direction is discussed. Extensive directional remagnetization is excluded as an explanation for the data. If stable directions obtained by alternating field remanence cleaning coincide with original TRM directions then a mean pole position for all temporally independent lava directions from the British Tertiary igneous province is at 71.9° N, 167.2° E, with k:22 and α₉₅:3.0°. This pole is significantly different from the geographic pole. If the difference in palaeomagnetic and geographic poles is interpreted in terms of absolute plate motion, then 2010 km of northwards motion of the western part of the Eurasian Plate, at 3.7 cm/yr, has taken place over the last 55 Myr. This motion has implications for the geological history of the Arctic and for the complexity of mantle motions.