Present day serpentinization in New Caledonia,Oman and Yugoslavia

Geochemical evidence for modern low-temperature serpentinization has been found in three new localities. Apparently the low-temperature reactions are a common mode of formation of the lizardite-chrysotile and brucite assemblage. Possibly the ¹⁸O content of serpentine formed at low temperatures is in part inherited from the pyroxene and olivine.     

Analysis of stellar occultation data: Effects of photon noise and initial conditions

A new inversion technique for obtaining temperature, pressure, and number density profiles of a planetary atmosphere from an occultation light curve is described. This technique employs an improved boundary condition to begin the numerical inversion and permits the computation of errors in the profiles caused by photon noise in the light curve. We present our assumptions about the atmosphere, optics, and noise and develop the equations for temperature, pressure, and number density and their associated errors. By inverting in equal increments of altitude, Δh, rather than in equal increments of time, Δt, the inversion need not be halted at the first negative point on the light curve as required by previous methods. The importance of the boundary condition is stressed, and a new initial condition is given. Numerical results are presented for the special case of inversion of a noisy isothermal light curve. From these results, simple relations are developed which can be used to predict the noise quality of an occultation. It is found that fractional errors in temperature profiles are comparable to those of pressure and number density profiles. An example of the inversion method is shown. Finally, we discuss the validity of our assumptions. In an appendix we demonstrate that minimum fractional errors in scale height determined from the inversion are comparable to those from an isothermal fit to a noisy isothermal light curve.     

Water vapor adsorption by sodium montmorillonite at −5°C

A large amount of interest has recently been expressed pertaining to the quantity of physically adsorbed water by the Martian regolith. Thermodynamic calculations based on experimentally determined adsorption and desorption isotherms and extrapolated to subzero temperatures indicate that physical adsorption of more than one or two monomolecular layers is highly unlikely under Martian conditions. Any additional water would find ice to be the state of lowest energy and therefore the most stable form. To test the validity of the thermodynamic calculations we have measured adsorption and desorption isotherms of sodium montmorillonite at ?5°C. To a first approximation it was found to be valid.     

A note on theH-functions of transfer problems in multiplying media

Some useful results and remodelled representations ofH-functions corresponding to the dispersion function $$T\left( z \right) = 1 - 2z^2 \sum\limits_1^n {\int_0^{\lambda r} {Y_r } \left( x \right){\text{d}}x/\left( {z^2 - x^2 } \right)} $$ are derived, suitable to the case of a multiplying medium characterized by $$\gamma _0 = \sum\limits_1^n {\int_0^{\lambda r} {Y_r } \left( x \right){\text{d}}x > \tfrac{1}{2} \Rightarrow \xi = 1 - 2\gamma _0< 0} $$      

Diffusion-deposition patterns in Martian streaks

The spreading angle of a number of light and dark Martian streaks is determined from selected Mariner 9 images. The resulting frequency distributions of spreading half-angles have maxima at ～5° for light, and ～7° for dark streaks; however the dark streaks have a secondary maximum spreading angle at ～14°. The smaller values, which include most streaks, are interpreted as crater-wake spreading phenomena. The larger value, found in only a few dark streaks or “tails,” may result from atmospheric diffusion and subsequent deposition of material from isolated sources such as vents or blowouts. An atmospheric diffusion-deposition analysis is presented, assuming this streak origin, from which it is possible to deduce the eddy diffusivity, K, in Mars' boudary layer. Calculated K values are found to agree with various theoretical estimates. They lie in the range 10⁷ and 10⁹ cm² sec^?1 and exhibit the proper scale dependence. Thus it appears that, in addition to streak-derived wind direction patterns and speed information, it is possible in a few cases to derive information on Mars' boundary-layer turbulence from streak-spreading measurements.     

Multiple frequency sounding of a Jovian cloud

Prior analysis of 20- and 45-μm flux measurements made from Pioneer 10 of broad regions near the Jovian equator revealed a cold longitudinal inhomogeneity (interpreted as a cloud obscuration) on the rising limb in the South Equatorial Belt. This feature appeared quite prominently at 45 μm and also at 5 μm in ground-based maps made simultaneously with the spacecraft measurements, but it does not appear at visible wavelengths. We describe a method by which the 5-μm observations are used to determine the fraction of 45-μm flux originating from only the region of the SEB obscured by this “anomalous” cloud. This allows the 45-μm data to constrain the cloud properties. On one extreme, the top of the SEB cloud was about 160°K, some 10°K warmer than a cloud in the neighboring South Tropical Zone, if the cloud was optically thick (nontransmissive). On the other hand, if the SEB cloud was as cool as the STrZ cloud, it must have been 60 to 80% transmissive, i.e., somewhat diffuse. With less uncertainty in the fraction of cloud obscuration, the ambiguity between tansmissivity and temperature is significantly diminished. The method described offers a potentially valuable tool for monitoring properties of clouds which do not necessarily appear at visible wavelengths.     

Upper limits to trace constituents in Jupiter's atmosphere from an analysis of its 5-μm spectrum

A high-resolution (0.6 cm^?1) spectrum of Jupiter at 5 μm recorded at the Kuiper Airborne Observatory is used to determine upper limits to the column density of 19 molecules. The upper limits to the mixing ratios of SiH₄, H₂S, HCN, and simple hydrocarbons are discussed with respect to current models of Jupiter's atmosphere. These upper limits are compared to expectations based upon the solar abundance of the elements. This analysis permits upper limit measurements (SiH₄), or actual detections (GeH₄), of molecules with mixing ratios with hydrogen as low as 10^?9. In future observations at 5 μm the sensitivity of remote spectroscopic analyses should permit the study of constituents with mixing ratios as low as 10^?10, which would include the hydrides of such elements as Sn and As as well as numerous organic molecules.     

A trigger mechanism for the emerging flux model of solar flares

The energetics of a current sheet that forms between newly emerging flux and an ambient field are considered. As more and more flux emerges, so the sheet rises in the solar atmosphere. The various contributions to the thermal energy balance in the sheet are approximated and the resulting equation solved for the internal temperature of the sheet. It is found that, for certain choices of the ambient magnetic field strength and velocity, the internal temperature increases until, when the sheet reaches some critical height, no neighbouring equilibrium state exists. The temperature then increases rapidly, seeking a hotter branch of the solution curve. During this dynamic heating, the threshold temperature for the onset of plasma microinstabilities may be attained. It is suggested that this may be a suitable trigger mechanism for the recently proposed emerging flux model of a solar flare.This work was done while the author was participating in the CECAM workshop on Plasma Physics applied to Active Solar Phenomena, August–September 1976 at Orsay, France, and the Skylab Solar Workshop on Solar Flares (sponsored by NASA and NSF and managed by the High Altitude Observatory).     

λ 5303 Fe XIV density models of the inner solar corona

The Sacramento Peak Observatory's 40 cm coronagraph was used with an emission line photometer to observe the distribution of 5303 Fe XIV brightness as a function of position angle, height above the limb, and time. These data were used to construct models of the volume emissivity as a function of solar latitude and longitude. These models in turn yield estimates of the distribution of electron density in the lower solar corona as a function of latitude and longitude for several specific periods in 1973 and 1975. Three observational results are obtained. An upper limit for the inferred electron density in coronal hole regions is set at log N _e = 7.4 for an altitude of 1.15R . Density models from late 1973 demonstrate an evolutionary trend toward a rather regular four-lobed appearance of coronal material; models from 1975 suggest that this characterization persisted for at least 27 solar rotations. A decrease in the total integrated 5303 intensity of a factor of 2.9 is inferred to have taken place between 1973 and 1975.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Effect of diffusion-thermal processes on the high-latitude topside ionosphere

We have studied the extent to which diffusion-thermal heat flow affects H⁺ temperatures in the high-latitude topside ionosphere. Such a heat flow occurs whenever there are H⁺?O⁺ relative drifts. From our study we have found that at high-latitudes, where H⁺ flows up and out of the topside ionosphere, diffusion-thermal heat flow acts to reduce H⁺ temperatures by 500–600 K at altitudes above about 900 km.