Coronal temperatures and temperature gradients from OSO-7 spectroheliograms

Temperatures and temperature gradients for the outer corona are obtained from brightness gradients of EUV lines that were measured with the spectroheliograph on OSO-7. Brightness gradients show considerable deviations from isothermal model calculations that include collisional excitation and photoexcitation. A negative temperature gradient that gives both positive and negative ion abundance gradients appears to be able to account for the discrepancy. For 284 of Fe xv, perhaps the strongest line from the outer corona, measurements during 1972 appear to be consistent with (i) a temperature near 2.3×10⁶K near the equator at = 1.3±0.1 solar radii from the solar center; (ii) (/T) dT/d values near -0.7 that extend from as low as = 1.2 to about = 1.8. Temperatures from strong lines of Fe xiv and Fe xvi indicate that variations of about ±0.2×10⁶K exist along lines of sight where emission is appreciable. There appears to be some agreement between these results and temperature measurements from ion abundances in the solar wind and Doppler width of 5303.     

The equatorial electrojet as detected from the abnormal electric current distribution above Huancayo,Peru, and elsewhere

Summary The abnormally large range of the daily variation of the horizontal (or north) component of magnetic force over Huancayo in Peru indicates the daily rise and decline of a concentrated eastward electric current above that station, superposed on the normal current distribution responsible for the daily magnetic variationS _q. The nameelectrojet is suggested for this concentrated current. New investigations indicate the occurrence of the electrojet also over Africa and India. To determine the height, intensity, width and return current flow of the electrojet, it is necessary to determine the abnormality in the daily range of the vertical (and perhaps also of the east) force, at stations north and south of the electrojet. It is suggested that the Bombay and Manila dailyZ variations already confirm the existence of the abnormality also in this element. Illustrative calculations are given that will be helpful in interpreting the proposed new data.

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Zusammenfassung Die außergewöhnlich große Amplitude der Tagesschwankung der Horizontal- (oder Nord-) Komponente der magnetischen Feldstärke über Huancayo (Peru) weist auf einen täglichen Anstieg und Abfall eines konzentrierten, nach Osten fließenden elektrischen Stromes oberhalb dieser Station hin, der der normalen Stromverteilung überlagert ist, auf die die magnetische TagesschwankungS _q zurückgeführt werden muß. Für diesen konzentrierten Strom wird die BezeichnungElektrostrahl (electrojet) vorgeschlagen. Aus neuen Untersuchungen läßt sich das Auftreten des Elektrostrahls auch über Afrika und Indien nachweisen. Um Höhe, Intensität, Breite und Rückfluß des Elektrostrahles zu berechnen, ist es notwendig, die Abweichungen der Tagesschwankung der Vertikal- (und eventuell auch der Ost-) Komponente der Feldstärke an Stationen nördlich und südlich des Elektrostrahls zu bestimmen. Es wird gezeigt, daß vielleicht bereits der Tagesgang der VertikalintensitätZ in Bombay und Manila das Auftreten dieser Anomalie auch bei diesem Element bestätigt; die notwendigen Berechnungen zum Verständnis dieser neuen Ergebnisse werden durchgeführt.

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Résumé L'amplitude anormalement grande de la variation diurne de la composante horizontale (ou nord) de l'intensité du champ magnétique à Huancayo (Pérou) semble indiquer l'augmentation et la diminution journalières d'un courant électrique concentré s'écoulant vers l'Est au-dessus de cette station et qui se superpose au courant normal auquel il faut attribuer la variation magnétique diurneS _q. On propose pour ce courant concentré le nom dejet électrique (electrojet). De récentes recherches permettent de retrouver également ce jet électrique au-dessus de l'Afrique et de l'Inde. Pour déterminer l'altitude, l'intensité, la largeur et la branche de retour du jet électrique, il faut mesurer les écarts de la variation diurne de la composante verticale (et éventuellement de la composante Est) de l'intensité du champ en des stations situées au Nord et au Sud du jet. On montre que peut-être la marche diurne de l'intensité verticaleZ à Bombay et à Manille révèle déjà cette anomalie de cet élément; on effectue les calculs nécessaires à la comprèhension de ces nouveaux résultats.

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With 13 Figures

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Research Associate, California Institute of Technology, April 1950 to March 1951, under Signal Corps Project No. 24-172B; on leave from Oxford University.     

The Al (Nb,Ta) Ti(in−2) substitution in titanite: the emergence of a new species?

Summary The highest (Nb, Ta) content ever encountered in titanite is reported from the Maríkov 11 pegmatite in northern Moravia, Czech Republic. This dike is a member of a pegmatite swarm of the beryl-columbite subtype, metamorphosed under conditions of the amphibolite facies. The pegmatite carries, i.a., rare tantalian rutile intergrown with titanian ixiolite, titanian columbite-tantalite, fersmite and microlite. Fissures generated in the Nb, Ta oxide minerals during deformation are filled with titanite, formed by reaction of the oxide minerals with metamorphic pore fluids. The titanite displays limited degrees of substitutions Na(Ta > Nb)(CaTi)_–1, (Ta > Nb)₄Ti_–4Si_–1 and AI(OH, F)(TiO)_–1, but an extensive (and occasionally the sole significant) substitution (Al > Fe³⁺)(Ta > Nb)Ti_–2, responsible for widespread oscillatory zoning. This substitution reduces the proportion of the titanite componentsensu stricto, CaTiSiO₄,O, to less than 50 mole % in many analyzed spots. The extreme composition corresponds to (Ca_0.994Na_0.011)(Ti_0.436Sn_0.007Al_0.280Fe³⁺ _0.006Ta_0.199Nb_0.079)Si_0.988O₄(O_0.974F_0.026). However, so far this substitution fails to generate compositions that would define a new species.

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Zusammenfassung Die AI(Nb, Ta)Ti_–2 Substitution im Titanit: Auftauchen einer neuen Mineralspecies? Die höchsten (Nb, Ta) Gehalte, die jemals für Titanit gefunden wurden, werden für den Maríkov II Pegmatit in Nordmähren, Tschechei, berichtet. Der Intrusivgang ist Teil eines Amphibolit-faziell überprägten Pegmatitschwarms vom Beryll-Columbit Subtypus Der Pegmatit führt u.a. seltene tantalbetonte Rutile verwachsen mit titanbetontem Ixiolith, titanbetontem Columbit-Tantalit, Fersmit and Mikrolith. Deformationsbedingte Frakturen in den (Nb, Ta) Oxiden sind mit Titanit, als Folge der Reaktion der metamorphen Porenlösungen mit den Oxidmineralen, verkittet. Titanit zeigt begrenzte Substitutionen Na(Ta > Nb)(CaTi)_–1,(Ta > Nb)₄Ti_–4Si_–1 and Al(OH, F)(TiO)_–1, aber extensive (und gelegentlich einzig bedeutsame) Substitution (Al >> Fe³⁺)(Ta > Nb)Ti_–2, die eine weitverbreitete, oszillierende Zonierung hervorruft. Diese Substitution verringert den Anteil der Titanit-Komponentesensu stricto, CaTiSiO,O, auf weniger als 50 Mol% in vielen Analysen. Die Extremzusammensetzung entspricht Ca_0.994Na_0.11) (T_10.436Sn_0.007Al_0.280Fe³⁺ _0.006Ta_0.199Nb_0.079)Si_0.988O₄(O_0.974F_0.026). Das AusmaB dieser Substitution ist unzureichend, um eine neue Mineralspecies zu definieren.

     

Editorial

A simulation of collisional and gravitational interaction in the early solar system generates planets ～500 km in diameter from an initial swarm of kilometer-sized planetesimals, such as might have resulted from gravitational instabilities in the solar nebula. The model treats collisions according to experimental and theoretical impact results (such as rebound, cratering, and catastrophic fragmentation) for a variety of materials whose parameters span plausible values for early solid objects. Ad hoc sticking mechanisms are avoided. The small planets form in ～10⁴ yr, during which time most of the mass of the system continues to reside in particles near the original size. The relative random velocities remain of the order of a kilometer-sized body's escape velocity, with random velocities of the largest objects somewhat depressed because of damping by the bulk of the material. The simulation is terminated when the largest objects' random motion is of smaller dimension than their collision cross sections, so that the “particle-in-a-box” statistical methods of the model break down. The few 500-km planets, in a swarm still dominated by kilometer-scale planetesimals, may act as “seeds” for the subsequent, gradual, accretional growth into full-sized planets.     

Modelling of scattering of seismic waves from a corrugated rough sea surface: a comparison of three methods

We compare three numerical methods to model the sea surface interaction in a marine seismic reflection experiment (the frequencies considered are in the band 10–100 Hz): the finite-difference method (FDM), the spectral element method (SEM) and the Kirchhoff method (KM). A plane wave is incident at angles of 0° and 30° with respect to the vertical on a rough Pierson–Moskowitz surface with 2 m significant wave height and the response is synthesized at 6, 10 and 50 m below the average height of the sea surface. All three methods display an excellent agreement for the main reflected arrival. The FDM and SEM also agree very well all through the scattered coda. The KM shows some discrepancies, particularly in terms of amplitudes.     

Actual and insolation-weighted Northern Hemisphere snow cover and sea-ice between 1973–2002

Actual and insolation-weighted Northern Hemisphere snow cover and sea ice are binned by latitude bands for the years 1973–2002. Antarctic sea-ice is also analyzed for the years 1980–2002. The use of insolation weighting provides an improved estimate of the radiative feedbacks of snow cover and sea-ice into the atmosphere. One conclusion of our assessment is that while a decrease in both areal and insolation-weighted values have occurred, the data does not show a monotonic decrease of either Arctic sea-ice or Northern Hemisphere snow cover. If Arctic perennial sea-ice is decreasing since the total reduction in areal coverage is relatively small, a large portion of it is being replenished each year such that its radiative feedback to the atmosphere is muted. Antarctic sea-ice areal cover shows no significant long-term trend, while there is a slight decrease in the insolation-weighted values for the period 1980–2002. From the early 1990s to 2001, there was a slight increase in both values. The comparison of general circulation model simulations of changes over the last several decades to observed changes in insolation-weighted sea-ice and snow cover should be a priority research topic.     

Horrocks, Crabtree and the 1639 transit of Venus

Now the deserved scientific and media excitement of the 2004 transit of Venus has passed, Allan Chapman offers a brief account of the career of Jeremiah Horrocks, who predicted and observed the 1639 transit.     

Some statistics concerning the daily geomagnetic character figureCp

Summary The frequency distribution ofCp over its range 0 to 2.5 has been determined and is discussed for groups of days selected according to (a) calendar month and (b) season (D, E, J)—1932–1965 inclusive—and for each of eleven year-groups selected in various ways on the basis of the annual mean sunspot number. For each group the median, mean and root-mean-square value ofCp has been found. The results favor the equinoctial hypothesis for the semi-annual variation of geomagnetic disturbance.