Oscillations of the Sun's chromosphere. VII. K grains revisited.

Details Oscillations of the Sun's chromosphere. VII. K grains revisited. Oscillations of the Sun's chromosphere. VII. K grains revisited.

Feb 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...294..252v&link_type=abstract

Astronomy and Astrophysics 294, 252-259 (1995)

Astronomy and Astrophysics

Astrophysics

57

Sun: Chromosphere, Sun: Oscillations Given

Scientific paper

We analyse time sequences of high spatial resolution filtergrams obtained simultaneously in Mg b_2_ and Ca K_2v_ from quiet Sun disc centre with the Vacuum Tower Telescope at Observatorio del Teide, Tenerife. Special attention is paid to the temporal evolution of the bright points, or K grains, in the interior of the chromospheric network. These represent the intensity maxima of brightness oscillations in K_2v_ with large amplitude. The oscillations last 1 to 5 periods of 150-240s duration and are strongly non-sinusoidal. They do not appear to be excited by pulses from below and then to decay. They rather exhibit the beat phenomenon of a horizontally extended wave field. The high amplitude oscillations occur only rarely, during 5-10% of the time, if we pose the limit that high amplitude means that the maximum intensity is a factor 1.5 larger than the average intensity. The power spectrum does not show any signature of a chromospheric "3 min" mode nor of a mode at the acoustic cutoff frequency (period 3.5min), nor do we find a power ridge at constant frequency. Instead, as in our earlier finding, the chromospheric oscillations are ordered in modes in continuation of the 5min modes. Modeling will thus need to adopt that the waves propagate in a three-dimensional medium with, at least partially, reflecting boundaries. The bright points of the chromospheric network behave very differently, more chaotic, like noise. They show most power at low frequencies which we interpret as the consequence of the stochastic intensity fluctuations.

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