Results 1 - 10 of 1716
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[en] The spread-F echoes on the vertical incidence ionograms at a temperate latitude station outside the equatorial F-region anomaly belt are shown to start with additional p'-f traces near the penetration frequencies due to off-vertical echoes. With time, these additional p'-f traces increase in intensity and in number, and extend to lower frequencies giving rise to range type of spread-F. The temperate latitude spread-F is suggested to arise mostly from the reflection of radio waves from the ripples and undulations in the iso-ionic surfaces in the ionosphere rather than from the scattering of radio waves from plasma instabilities. These characteristics are thus very different from the development of spread-F at equatorial stations
[en] The annual wave of the magnetic activity is the resultant of various components. The first one has its maximum during the summer solstice of each hemisphere and is caused by additional activity, especially in H component, around 15 h LT; its amplitude varies with longitude, and is largest on the meridian of each magnetic pole in each hemisphere; it seems to be larger in the Northern hemisphere than in the Southern one. The second component is driven by the sin2 psisub(M) - modulation of the magnetic activity (McIntosh effect; psisub(M) is the angle between the solar wind and the dipole axis); its amplitude varies in the same way in both hemispheres with longitude; it is largest (or null) at longitudes where the maximum of the local time daily variation of the activity is close to 4.5 h and 16.5 h UT (or 10.5 and 22.5 h UT); its annual maximum (or minimum) is at June solstice when the daily maximum of the activity occurs between 22.5 and 10.5 h UT (or between 10.5 h and 22.5 h UT). The existence of these two components is unquestionable. A third component would correspond to a larger activity around (or after) the local midnight during the winter solstice than during the summer solstice. With planetary indices based upon a very dense network of observatories which has a perfectly uniform longitude distribution, only the second component would be perfectly compensated
[fr]L'onde annuelle de l'activite magnetique est formee de diverses composantes. L'une a son maximum au solstice d'ete de chaque hemisphere et est causee par un supplement d'activite, surtout sur la composante horizontale H, autour de 15 h TL; son amplitude varie en longitude, et est la plus grande sur le meridien des poles; elle semble etre plus grande dans l'hemisphere Nord que dans l'hemisphere Sud. L'autre est induite par la modulation en sin2 psisub(M) de l'activite magnetique (effet McIntosh; psisub(M) est l'angle entre axe du dipole et direction du vent solaire); son amplitude varie de la meme maniere dans les deux hemispheres en fonction de la longitude; elle est la plus grande (ou est nulle) sur les longitudes ou le maximum journalier en temps local de l'activite aux equinoxes est proche de 4.5 h et 16.5 h TU (ou 10.5 et 22.5 h TU); elle a son maximum (ou son minimum) au solstice de juin selon que le maximum journalier est compris entre 22.5 et 10.5 h TU (ou entre 10.5 et 22.5 h TU). Une troisieme composante correspondrait a une activite plus grande autour (ou apres) du minuit local pendant le solstice d'hiver que pendant le solstice d'ete. Sur des indices planetaires bases sur un reseau d'observatoires tres dense et parfaitement uniforme quant a sa distribution en longitude, seule la deuxieme composante serait parfaitement compensee
[en] It is shown that if the one-year oscillation in the drift of sunspots in the latitude and the longitude is attributed to inaccuracies in the values used for Ω (the longitude of the ascending node of the solar equator on the ecliptic) and I (the inclination of the solar equator to the ecliptic), the value used for Ω is found to be about 3deg higher and the value used for I about 3deg too small. It seems improbable that such errors could exist. (author)
[en] Complete text of publication follows. Beyond all manner of doubt geomagnetic secular variations (SV) consist of internal and external components. We calculated SV(H) as a difference between mean yearly values of the horizontal component on all days for magnetic observatories Belsk (BEL), Lviv (LVV), Leningrad (LNN). The same was performed by using only mean yearly values H on five international quiet days for every month. Comparison between the results fulfilled. Long and short period SV(H) variations at all observatories for both cases don't differ considerably. We search of the explanation for such phenomenon.
[en] Scattered lights from terrestrial exoplanets provide valuable information about their planetary surface. Applying the surface reconstruction method proposed by Fujii et al. to both diurnal and annual variations of scattered light, we develop a reconstruction method of land distribution with both longitudinal and latitudinal resolutions. We find that one can recover a global map of an idealized Earth-like planet on the following assumptions: (1) cloudlessness, (2) a face-on circular orbit, (3) known surface types and their reflectance spectra, (4) lack of atmospheric absorption, (5) known rotation rate, (6) a static map, and (7) the absence of a moon. Using the dependence of light curves on planetary obliquity, we also show that the obliquity can be measured by adopting the χ2 minimization or the extended information criterion. We demonstrate the feasibility of our methodology by applying it to a multi-band photometry of a cloudless model Earth with future space missions such as the occulting ozone observatory (O3). We conclude that future space missions can estimate both the surface distribution and the obliquity at least for cloudless Earth-like planets within 5 pc.