A gradient-based method of tessellation was applied to SOHO Dopplergrams and to Ca II K Ðltergrams in order to study the cellular pattern of the solar surface, in speciÐc the geometric relationship between the tessellation and the chromospheric network/supergranulation. We found that for zero spatial smoothing and low temporal averaging the above data sets yield mean tessellation scales of 8È10 Mm for the SOHO Dopplergrams of 2A pixel resolution and 14È18 Mm for K line Ðltergrams of 3A .2 pixel resolution. This di †erence is attributed to the dependence of the tessellation on the resolution of the images. The distribution of the tessellating tiles shows a broad, right-skewed spectrum, tending to greater broadness, symmetry, and larger scales when the image is smoothed. The skewness and kurtosis curves of the distribution of the tiles as a function of the smoothing show local peaks when the mode of the distribution approaches the traditional supergranular scale of 25 Mm. The values of skewness and kurtosis in this limit, 1.1 and 4.6, respectively, are close to the corresponding parameters for supergranular distribution derived independently, implying that supergranulation may be geometrically identi-Ðed with the tessellation at the corresponding resolution. Time averaging also leads to an increase in length scale when averaged for up to 30 hr. In the case of Dopplergrams the size increases from 9 to 16 Mm and for the K line Ðltergrams from 18 to 23 Mm. This feature can be attributed to the suppression of short-lived, small-scale features. The e †ects of both spatial smoothing and temporal averaging can be explained in terms of enhancement of the supergranular signal.
The coronal green line (Fe XIV 5303Å) profiles were obtained from Fabry-Perot interferometric observations of the solar corona during the total solar eclipse of 21 June 2001 from Lusaka, Zambia. The instrumental width is about 0.2Å and the spectral resolution is about 26000. About 300 line profiles were obtained within a radial range of 1.0-1.5 R ⊙ and position angle coverage of about 240 • . The line profiles were fitted with single Gaussian and their intensity, Doppler velocity, and line width have been obtained. Also obtained are the centroids of the line profiles which give a measure of line asymmetry. The histograms of Doppler velocity show excess blueshifts while the centroids reveal a pre-dominant blue wing in the line profiles. It has been found that the centroids and the Doppler velocities are highly correlated. This points to the presence of multiple components in the line profiles with an excess of blueshifted components. We have then obtained the(Blue-Red) wing intensity which clearly reveals the second component, majority of which are blueshifted ones. This confirms that the coronal green line profiles often contain multicomponents with excess blueshifts which also depend on the solar activity. The magnitude of the Doppler velocity of the secondary component is in the range 20-40 km s −1 and they show an increase towards poles. The possible explanations of the multicomponents could be the type II spicules which were recently found to have important to the coronal heating or the nascent solar wind flow, but the cause of the blue asymmetry in the coronal lines above the limb remains unclear.
Instability of themocovection in a multi-component fluid has wide range of applications in ionospheric, geothermal and industries. In this analysis, the effect of rotation and vertical anisotropy on Soret-driven thermoconvective instability in a ferrofluid has been studied. The fluid layer is assumed to be horizontal and is heated from below and salted from above. In momentum equation, the effect of both substantial derivatives and coriolis terms are considered. The resulting eigen value problem is solved using Brinkman model. A linear stability analysis is used for both stationary and oscillatory instabilities for different parameters for which normal mode technique is applied. The effect of rotation tends to stabilize the system and anisotropy and Soret effects tend to destabilize the system.
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