Velocity and vorticity measurements of Jupiter's Great Red Spot using automated cloud feature tracking

We have produced mosaics of the Great Red Spot (GRS) using images taken by the Galileo spacecraft in May 2000, and have measured the winds of the GRS using an automated algorithm that does not require manual cloud tracking. Our technique yields a high-density, regular grid of wind velocity vectors that is advantageous over a limited number of scattered wind vectors that result from manual cloud tracking. The high-velocity collar of the GRS is clearly seen from our velocity vector map, and highest wind velocities are measured to be around 170 m s⁻¹. The high resolution of the mosaics has also enabled us to map turbulent eddies inside the chaotic central region of the GRS, similar to those mapped by Sada et al. [Sada, P.V., Beebe, R.F., Conrath, B.J., 1996. Icarus 119, 311-335]. Using the wind velocity measurements, we computed particle trajectories around the GRS as well as maps of relative and absolute vorticities. We have discovered a narrow ring of cyclonic vorticity that surrounds the main anti-cyclonic high-velocity collar. This narrow ring appears to correspond to a ring surrounding the GRS that is bright in 5 μm [Terrile, R.J., Beebe, R.F., 1979. Science 204, 948-951]. It appears that this cyclonic ring is not a transient feature of the GRS, as we have discovered it in a re-analysis of Galileo data taken in 1996 first analyzed by Vasavada et al. [Vasavada, A.R., and 13 colleagues, 1998. Icarus 135, 265-275]. We also calculate how absolute vorticity changes as a function of latitude along a trajectory around the GRS and compare these measurements to similar ones performed by Dowling and Ingersoll [Dowling, T.E., Ingersoll, A.P., 1988. J. Atmos. Sci. 45, 1380-1396] using Voyager data. We show no dramatic evolution in the structure of the GRS since the Voyager era except for additional evidence for a counter-rotating GRS core, an increase in velocity in the main velocity collar, and an overall decrease in the length of the GRS.     

The disappearance of OH from comet P/Encke

Photoelectric observations of Comet P/Encke during its 1980 apparition are combined with other published data to relate molecular production rates to the visual lightcurve. In addition to a substantial asymmetry about perihelion which is already well known, there are shorter-term variations in specific molecules which have not been duplicated by models. The most dramatic of these fluctuations is a rapid decrease by more than a factor of 3 in the production of OH at 0.75 AU preperihelion.     

Density fronts in the vicinity of a long ridge

Laboratory experiments concerning the nature of density fronts in a two-layer fluid in the vicinity of a continuous ridge were conducted. The experiments were carried out in a circular rotating test cell containing an annular ridge of uniform cross-section. The density fronts were established by releasing a lighter fluid contained in a bottomless cylinder in the interior of the region defined by the topography into a heavier fluid occupying the rest of the test cell. The system was also equipped with an oscillating plunger located along the test cell axis to produce simulated tidal currents impinging in the normal direction on the ridge; experiments without and with tidal forcing were conducted. The governing parameters for the physical system considered are the Rossby, temporal Rossby, Burger and Ekman numbers and geometrical parameters. It is found that for both the non-forced and tidally forced experiments the fronts were stabilized by the ridge. The fronts in the simulated tidal currents experiments were found to advect radially outward more rapidly at early times than their non-forced counterparts; at large times, the temporal evolution of the front for these forced experiments approached that of the non-forced experiments. In the region interior to the annular ridge, the motion field is highly baroclinic, while outside this region, the flow response at the forcing frequency is barotropic. Scaling arguments regarding frontal position, viscous decay and barotropic oscillatory flow responses are advanced and supported by experimental observations.     

Chemical interdiffusion of dacite and rhyolite: anhydrous measurements at 1 atm and 10 kbar,application of transition state theory,and diffusion in zoned magma chambers

Chemical diffusivity measurements have been made on anhydrous metaluminous diffusion couples of dacite and rhyolite at 1 atm, 1200°–1400° C, and 10 kbar, 1300°–1600° C, and on anhydrous peraluminous and peralkaline dacite-rhyolite diffusion couples at 10 kbar, 1300°–1600° C. Chemical diffusivities for Si, Al, Fe, Mg, and Ca were measured in all experiments on the metaluminous diffusion couples using Boltzmann-Matano analysis, and Si diffusivities were measured on the other diffusion couples. Two 10 kbar metaluminous experiments were analyzed with the X-ray microprobe and diffusivities of Sr, Y, Zr and Nb were measured. Si diffusivity displays a weak negative correlation with SiO₂ content over the range of 65%–75% SiO₂. At a given SiO₂ content chemical diffusivities of all non-alkali elements are usually within less than an order of magnitude of Si chemical diffusivity and are controlled by partitioning along the diffusion profile so as to maintain local equilibrium at each point along the profile. Alkali chemical diffusivities were not measured but can be estimated from the experiments to be orders of magnitude higher than non-alkali chemical diffusivities. Data were fit to Arrhenius equations for diffusivities measured at 65, 70 and 75% SiO₂. At 1 atm the Arrhenius equation for non-alkalies at 70% SiO₂ in the metaluminous system is:

Time variation of martian regional contrasts

Observations of contrast changes in blue light on Mars in 1969 and 1971 are presented. Seasonal effects evidently can be evaluated from these data, although nonseasonal effects are also present. A diurnal variation is noted for certain features during both apparitions. This variation cannot be fully accounted for without considering meteorological effects. An example of a contrast reversal in ultraviolet light is presented. The suggestion is made that during the Martian season covered herein, variability of the bright areas controlled the apparent contrasts observed.     

The biogeochemical fate and toxicity of mercury in Controlled Experimental Ecosystems

The affinity of mercury for organic matter was the most important parameter governing its chemical speciation, transport and toxicity in Controlled Experimental Ecosystems (CEEs) of the Controlled Ecosystem Pollution Experiment (CEPEX) deployed in Saanich Inlet, B.C., Canada, Particulate, colloidal and high molecular weight dissolved forms of mercury accounted for about 90% of the total mercury present in the water column. Bioassays indicated that organic matter in the above size classes had an important influence on the toxicity of mercury to phytoplankton.Sorption of mercury to particulate organic matter in the CEEs could be described by either Freundlich or linear adsorption isotherms. An observed depth-dependent increase in mercury content of particulate matter was attributed to selective biological degradation of non-mercury-binding organic components of the particles during settling.The high affinity of mercury for settling particulate organic matter led to rapid removal of mercury from CEEs. Removal rates could be described as first order and were a function of primary production rates. Deviations of measured half-removal times from those predicted by an empirically formulated relationship between primary production and mercury half-removal times could be related successfully to the influence of other occasionally significant biological parameters such as zooplankton grazing activity.