Energy transfer by magnetopause reconnection and the substorm parameter ϵ

An expression for the magnetopause reconnection power based on the dawn-dusk component of the reconnection electric field, that reduces to the substorm parameter ? for the limit that involves equal geomagnetic (B_G) and magnetosheath (B_M) magnetic field amplitudes at the magnetopause, is contrasted with the expression based on the whole reeonnection electric field vector (Gonzalez, 1973). The correlation examples of this report show that this (more general) expression for the reconnection power seems to correlate with the empirical dissipation parameter U_T (Akasofu, 1981), with slightly better correlation coefficients than those obtained from similar correlations between the parameter ? and U_T Thus, these (better) correlations show up for the more familiar values of the ratio B_G/B_M > 1. Nevertheless, the (expected) relatively small difference that seems to exist between these correlation coefficients suggests that, for practical purposes, the parameter ? could be used as well (instead of the more general expression) in similar correlation studies due to its simpler format. On the other hand, studies that refer mainly to the difference in the magnitudes of ? and of the more general expression are expected to give results with less negligible differences.     

Gradient de densité et température dans la basse couronne

Résumé On considère souvent que le milieu coronal est en équilibre hydrostatique si bien que l'étude de la distribution verticale de la matière est censée donner une bonne estimation de la température coronale (Billings, 1966). De fait, le gradient vertical de densité observé dans la basse couronne (altitudes inférieures à 300 000 km) où l'effet du vent solaire est peu important conduit à une température hydrostatique de 1 500 000 K en moyenne, en assez bon accord avec les déterminations fondées sur l'étude du rayonnement radioélectrique et sur celle de l'ionisation. Il semblerait néanmoins souhaitable de chercher à préciser cette concordance moyenne en comparant dans le détail les variations de la température coronale et celles du gradient vertical de densité pour voir si l'hypothèse de l'équilibre hydrostatique est partout vérifiée.Cette comparaison ne peut être tentée qu'à partir d'un jeu d'observations suffisamment variées pour que l'on puisse déterminer de façon indépendante la densité et la température dans une même région de la couronne: un tel matériel est disponible grâce aux observations coronales effectuées entre 1967 et 1969 à l'Observatoire du Pic du Midi, qui comportent notamment, pour 81 journées d'observations, (a) la mesure de l'intensité des raies 5303 Å et 6374 Å, à 1 du bord, tous les 5° autour du Soleil (b) la mesure de la brillance de la couronne K pour les mêmes angles de position, à 15 et à 5 du bord. Sans discuter ici des caractéristiques propres à ces deux catégories d'observations, qui ont déjà été décrites dans d'autres publications, nous allons chercher dans ce travail à les utiliser pour mettre à l'épreuve la validité de l'hypothèse de l'équilibre hydrostatique dans la basse couronne.

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The observations performed at the Pic du Midi Observatory with a K-coronameter at different altitudes above the solar limb allow us to compute the vertical density gradient of the corona, therefore giving the value of the hydrostatic temperature T _h computed under the assumption of hydrostatic equilibrium in the lower corona. We compare T _h with the ratio r = I ₅₃₀₃/I ₆₃₇₄ of the intensities of the green and the red coronal lines observed at the same position angle and on the same day: r is expected to yield the proportion of cold regions and hot regions along the line of sight under study. As a matter of fact no relation appears between individual values of T _h and r nor between averaged values of T _h and r (Figure 1). In a second step we compute the 5303 Å emission which should be observed, for selected position angles where 6374 Å emissions are faint, making use of the electron density values which can be deduced from the K corona observations. The ratio q = (I ₅₃₀₃) obs/(I ₅₃₀₃) calc of observed to computed 5303 Å intensities should depend upon the corona temperature according to the ionization theory. But again, we do not find the expected relation since Figure 2 displays only a large scatter of points. We conclude that large deviations to hydrostatic equilibrium probably occur in the corona but it is still possible that the presence of arch structures in the lower corona makes it unrealistic to interpret a ratio of intensities integrated along different lines of sight in term of a regular density gradient, although this procedure has been universally used up to now.

     

Gravity and seismicity analyses of the El Chichon volcano,Chiapas, Mexico

Subduction induced compressional stress, lateral displacement faults probably linked to the NW extension of the Polochic-Motagua fault system, and local magma emplacement create a complex geological setting for the El Chichon volcano.Gravity analysis reveals that the principal structures in the area correspond to synclines and anticlines. Downward continuation of the gravity field suggests the presence of magma emplacement SE of the volcano. This magmatic emplacement appears to be the principal cause of the truncation of the syncline in which the volcano lies.Analyses of earthquakes occurring after eruptions show that the vertical distribution of events is confined to a roughly cylindrical zone which correlates well with the region of magmatic emplacement inferred from the gravity analysis.Even though more than 350 km separate the volcano from the Middle American trench, the compressional stress regime reported for the area may correlate with subduction stress (N30°E). However, the strike direction for the principal faults in the zone, N60°W, permits us to postulate that the NW extension of the Polochic-Motagua fault system is implicated in the local tectonics of the El Chichon area.     

Parent stars of extrasolar planets – VIII. Chemical abundances for 18 elements in 31 stars

We present the results of detailed spectroscopic abundance analyses for 18 elements in 31 nearby stars with planets (SWPs). The resulting abundances are combined with other similar studies of nearby SWPs and compared to a sample of nearby stars without detected planets. We find some evidence for abundance differences between these two samples for Al, Si and Ti. Some of our results are in conflict with a recent study of SWPs in the SPOCS data base. We encourage continued study of the abundance patterns of SWPs to resolve these discrepancies.     

Biogeochemical aromatic markers in the sediments from mahakam delta (Indonesia)

Analysis of the tri-, tetraand pentaaromatic hydrocarbon fractions of several sediments (0–600 m) from the Mahakam Delta (Indonesia), indicate the predominance of polycyclic aromatic hydrocarbons (PAH) diagenetically related to triterpenoid natural precursors. High resolution Shpol'skii spectrofluorometry (HRS) proved to be a valuable analytical tool, in conjunction with high performance liquid chromatography (HPLC) and capillary gas chromatography coupled with mass spectrometry (CGC/MS), for the identification of individual components in Chromatographic fractions obtained after a high resolution reverse phase liquid chromatography.     

Transition probabilities and dissociation energy of astrophysical molecule CoH

The Franck-Condon (FC) factors (transition probabilities) and r-centroids have been evaluated by the reliable numerical integration procedure for the bands of the A ³ φ₄ →X ³ φ₄ system of astrophysical molecule CoH, using a suitable potential. The dissociation energy D ⁰ ₀ = 2.5 ± 0.05 eV for the electronic ground state of CoH has been estimated by fitting Hulburt-Hirschfelder function to the experimental potential energy curve, using the correlation coefficient. This revised version was published online in July 2006 with corrections to the Cover Date.     

Biodegradation of Herbicide Propanil and Its Subproduct 3,4‐Dichloroaniline in Water

The rational use of pesticides generates an impact which is normally reversed and eliminated by the environment itself. However, the indiscriminate use of pesticides makes its natural degradation rhythm difficult, prolonging their presence in the soil for a great deal of time. Aiming towards a decrease in the environmental impact of pesticides, soil microorganisms capable of degrading pesticides, such as propanil, were investigated. An Enterobacter cloacae strain, isolated from rice field soil, was exposed to the herbicide propanil alone and in a mixture containing also bentazone, clomazone, quinclorac, and 2,4‐D. This bacterium was able to eliminate 100% of the applied propanil in 28 days. Propanil degradation in the 5‐herbicide mixture was much lower than that of individual pesticide degradation. The aeration of the system helped to degrade propanil and its subproduct 3,4‐dichloroaniline much faster. LC with UV detection was used to determine the remaining concentrations of the herbicides and their subproducts.     

Relative importance of ozone energy transfer processes in the middle and upper atmosphere

The relative importance of different processes and transitions in the appearance of non-LTE populations for the fundamental levels of ozone was studied by quantifying the kinetic law of every process and transition that affect each level population. The vibrational temperatures and the relative contribution of every transition are presented as a function of altitude. The results show that the appearance of non-LTE populations for the fundamental levels is not produced by a direct imbalance between absorption and emission but as a consequence of imbalanced collisional transitions provoked by the overpopulation of O₃(0 v₂ 0) levels. This fact confirms that the relaxation cascade drives through the bending mode ν₂.     

Tectonic shortening and gravitational spreading in the Gulf of Cadiz accretionary wedge: Observations from multi-beam bathymetry and seismic profiling

The Gulf of Cadiz lies astride the complex plate boundary between Africa and Eurasia west of the Betic-Rif mountain belt. We report on the results of recent bathymetric swathmapping and multi-channel seismic surveys carried out here. The seafloor is marked by contrasting morphological provinces, spanning the SW Iberian and NW Moroccan continental margins, abyssal plains and an elongate, arcuate, accretionary wedge. A wide variety of tectonic and gravitational processes appear to have shaped these structures. Active compressional deformation of the wedge is suggested by folding and thrusting of the frontal sedimentary layers as well as basal duplexing in deeper internal units. There is evidence for simultaneous gravitational spreading occurring upslope. The very shallow mean surface and basal slopes of the accretionary wedge (1° each) indicate a very weak decollement layer, geometrically similar to the Mediterranean Ridge accretionary complex. Locally steep slopes (up to 10°) indicate strongly focused, active deformation and potential gravitational instabilities. The unusual surface morphology of the upper accretionary wedge includes “raft-tectonics” type fissures and abundant sub-circular depressions. Dissolution and/or diapiric processes are proposed to be involved in the formation of these depressions.