The Photospheric Convection Spectrum     

Hathaway  D.H.  Beck  J.G.  Bogart  R.S.  Bachmann  K.T.  Khatri  G.  Petitto  J.M.  Han  S.  Raymond  J. 《Solar physics》2000,193(1-2):299-312

Spectra of the cellular photospheric flows are determined from observations acquired by the MDI instrument on the SOHO spacecraft. Spherical harmonic spectra are obtained from the full-disk observations. Fourier spectra are obtained from the high-resolution observations. The p-mode oscillation signal and instrumental artifacts are reduced by temporal filtering of the Doppler data. The resulting spectra give power (kinetic energy) per wave number for effective spherical harmonic degrees from 1 to over 3000. Significant power is found at all wavenumbers, including the small wavenumbers representative of giant cells. The time evolution of the spectral coefficients indicates that these small wavenumber components rotate at the solar rotation rate and thus represent a component of the photospheric cellular flows. The spectra show distinct peaks representing granules and supergranules but no distinct features at wavenumbers representative of mesogranules or giant cells. The observed cellular patterns and spectra are well represented by a model that includes two distinct modes – granules and supergranules.  相似文献   

Fe(II) adsorption on hematite (0 0 0 1)     

Kunaljeet S. Tanwar  Sarah C. Petitto  Peter J. Eng 《Geochimica et cosmochimica acta》2009,73(15):4346-2587

The surface structure of α-Fe₂O₃(0 0 0 1) was studied using crystal truncation rod (CTR) X-ray diffraction before and after reaction with aqueous Fe(II) at pH 5. The CTR results show the unreacted α-Fe₂O₃(0 0 0 1) surface consists of two chemically distinct structural domains: an O-layer terminated domain and a hydroxylated Fe-layer terminated domain. After exposing the α-Fe₂O₃(0 0 0 1) surface to aqueous Fe(II), the surface structure of both co-existing structural domains was modified due to adsorption of Fe at crystallographic lattice sites of the substrate, resulting in six-coordinated adsorbed Fe at the surface. The average Fe-O bond lengths of the adsorbed Fe are consistent with typical Fe(III)-O bond lengths (in octahedral coordination), providing evidence for the oxidation of Fe(II) to Fe(III) upon adsorption. These results highlight the important role of substrate surface structure in controlling Fe(II) adsorption. Furthermore, the molecular scale structural characterization of adsorbed Fe provides insight into the process of Fe(II) induced structural modification of hematite surfaces, which in turn aids in assessing the effective reactivity of hematite surfaces in Fe(II) rich environments.  相似文献