Umbral oscillations in the presence of a spreading magnetic field

Résumé Des onze observatoires qui, depuis 1947, ont à des degrés divers participé à l'obtention de données coronales au coronographe, six seulement sont encore en service. Rendues homogènes à partir d'un traitement statistique, ces données permettraient de couvrir trente cinq années d'activité solaire, soit près de quatre cycles complets. Une exploitation intéressante de ces mesures est la recherche des trous coronaux (autre que polaires), sources du vent solaire à haute vitesse dont les retombées en matière d'accroissement de nos connaissances sur la physique de la haute atmosphère et relations avec le climat terrestre sont primordiales. De nombreuses résolutions récentes de symposium ont conclu en ce sens et il serait bon que les commissions spécialisées concernées de l'UAI se prononcent sur ce problème au cours de l'une de ses prochaines réunions.

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Thirty-five years of patrol measurements of the intensity of the solar corona outside eclipses

A review of the various observatories having done daily measurements of the activity of the solar corona and having regularly published their results is being given hereby. Out of eleven observatories having taken out to the observation campaign since 1947, only six are still working in this field. Due to the fact that the scales, the focus and photometric systems are not always the same, the measurements are not homogeneous and directly comparable. However, astronomers can find there a great lot of statistical data covering thirty five years of coronal activity, that is more than three solar cycles. Some of these data, such as those of the Pic-du-Midi observatory, are readily available on magnetic tapes and may be asked from the authors. One of the most interesting exploitations of these data is the search of coronal holes (other than polar holes which are simply the signature of the periodic activity of corona) and it is shown here that such features are easily detectable. So, it will be vital for future research in solar physics, and especially in solar weather and climate relationships (bearing in mind that coronal holes are the sources of high speed streamers of the solar wind which interacts with the Earth magnetosphere), to ensure continuity and quality of patrol ground-based corona intensities outside eclipses. A number of recent conclusions of symposia in this field have led to such recommendations, and it would be suitable if next specialized commissions of IAU meetings were to think about that matter.