ABSTRACT:The paper presents the analysis of field measurements in the atmospheric surface layer over the floor of the Adige Valley, near the city of Bolzano in the Alps. Turbulence quantities, such as drag coefficient, displacement height and roughness length, appear similar to those reported in the literature concerning surface-layer turbulence over flat uniform terrain. The analysis of the non-dimensional standard deviations (σ u , σ v , σ w ) legitimates the adoption, for all the wind components, of the same Monin-Obukhov similarity relationship in the form σ i /u * = α i (1 + β i |ζ |) 1/3 , originally proposed only for flat uniform terrain under steady state conditions, and the extension of this expression to the case of winds over a valley floor in slowly varying situations. The coefficients α i are very similar for along-valley and cross-valley winds, as are the β i ones. Moreover the α u values are only slightly larger than the α v , contrary to what is reported in the literature. Conversely, σ θ /θ * shows distinctly different behaviour in the stable and unstable regimes. In particular, in the latter case a large scatter in the data is observed. However, since the most scattered data turn out to occur in transition periods (i.e. sunrise and sunset), after a specific data selection the best-fit parameters are more accurately estimated. In addition, emphasis is laid on the relevance of an appropriate formulation and use of a suitable recursive filter to separate the low-frequency unsteadiness of the mean flow from the turbulence signal.

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Ferromagnetic particulate matter from various volcanic areas has been compared with black magnetic spherules (b.m.s.) sampled in air and in marine sediments. The following main differences have been recognized: (1) in the volcanic ash deposits, ferromagnetic spherules neither solid nor hollow are found; only magnetite crystals usually associated with silicate fragments have been observed; (2) the volcanic ferromagnetic particles and the b.m.s. have similar Fe contents but different contents of minor elements, the former yielding Si, AI, Ti, Ca, Mg, and Cr, and the latter, Ni, Co, and It; and (3) while the b.m.s. have a polycrystalline structure characterized by a magnetite, wiistite, and a-Fe paragenesis, the volcanic particles are composed only of magnetite and are often in monocrystalline form. Thermodynamic considerations agree with the experimental results showing that the b.m.s. cannot have a volcanic origin. 0000 * * ß O O O O ß ß ß 0 00

Laboratory experiments of melting and cooling of Fe and Fe 90%–Ni 10% particles in atmospheres of both air and single‐gas species whose vapor pressures varied in the range 20–760 mm Hg are reported. The process that extraterrestrial ferromagnetic particulate matter in the range 4–250 μm undergoes during its flight through the atmosphere is reproduced. The results of our laboratory experiments indicate that cavities form as a result of complete oxidation of particles accompanied by a strong decrease in oxygen solubility and that natural black magnetic spherules are similar in mineralogic association and texture to artificial ones produced at low O2 pressure.