Документ взят из кэша поисковой машины. Адрес оригинального документа : http://star.arm.ac.uk/~ambn/abstract280.html Дата изменения: Mon Feb 2 18:56:41 1998 Дата индексирования: Tue Oct 2 00:23:42 2012 Кодировка: Поисковые слова: http astrokuban.info astrokuban

The power specta for line intensities of several lines formed in the upper transition region around 100,000 to 250,000K are presented. A period of ~5 min. is clearly present in lines due to O III, O IV and O V. In one dataset a period approaching 10 min. is present for ~10 min. The size of the emitting features is limited to ~7 arcsec squared. In all datasets examined, there is excess power below 1mHz everywhere along the slit, although the observed periods do not always come from the most intense regions. In ~10% of instances clear periods are observable in the 2-5mHz range with the largest power peak at 3.0mHz. In all regions, the 5.0mHz power peak is smaller. For the frequencies investigated there are no significant time delays in any of the datasets examined. This finding may not be entirely unexpected as the formation temperatures of O III (~100,000K) and O V (~250,000K) may be too close in order to result in an observable phase shift. The observations are discussed in terms of trapped magnetic modes below the transition region and resoant absorption of MHD waves. For resonant absorption we derive from the observed period of 5 minutes and the observed extent of the structure a typical magnetic field strength of about 2 Gauss. This value is in good agreement with results from MDI for quiet Sun regions. Our results seem to imply that resonant waves can play a role in the heating of the quiet Sun. We discuss the effect of observing without tracking on the power spectrum and show that the effect is small.