Astronomy and Astrophysics – Astrophysics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sp41b02a&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SP41B-02
Astronomy and Astrophysics
Astrophysics
7500 Solar Physics, Astrophysics, And Astronomy, 7529 Photosphere, 7594 Instruments And Techniques
Scientific paper
We address the evolutionary behavior of the granulation dynamics from an observational point of view by analyzing a series of excellent spectrograms taken at the VTT in Izaña/Tenerife (Spain) in 1999. We present temporal-spatial maps of the Doppler velocity, turbulent line broadening, and intensity variations, which allow us to study the dynamical behavior of these observables at different positions on the solar surface. The Doppler velocity maps reveal a granular dynamical time -- the time associated with the Doppler velocity decay -- of approximately 2 min, while the turbulence map does not show any characteristic time but a strong intermittency. The intensity map reveals the life time of the granulation as it is given in the literature. The granular dynamical time is practically equal to the value determined from spectrograms taken during the solar minimum in 1994; so the dynamical time does not show any change over half a solar cycle. The stochastical properties of the Doppler velocity and intensity data samples were studied (i) by means of their statistical moments and (ii) by using theoretically model distributions. For the latter we estimated the distributions' parameters by means of the maximum likelihood method. The histograms of the Doppler velocity variations point to an asymmetrical model distribution, while the histograms of the intensity variations infer a symmetrical one. Thus the intensity variations can be described well by a Gaussian probability density function, while the Doppler velocity variations can be described by a Gumbel distribution an asymmetrical probability function. A remarkable result of the statistical analysis of both the observations from 94 and 99 is the unambiguous lack of flows with large velocity amplitudes within the intergranular space.
Anastasios N.
Helmhold S.
Markus R.
Reiner Hannes
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