Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999a%26a...349..301r&link_type=abstract
Astronomy and Astrophysics, v.349, p.301-311 (1999)
Astronomy and Astrophysics
Astrophysics
41
Sun: Atmosphere, Sun: General, Sun: Granulation, Sun: Photosphere
Scientific paper
We analyse the two algorithms which have been used in the past few years to determine the horizontal flow fields at the Sun's surface, namely the Local Correlation Tracking (LCT) of L. November and the Feature Tracking of L. Strous. Analysing the systematic errors introduced by LCT, we show that these errors come from the averaging processes. More precisely, they arise from the interpolating step of the algorithm: granules' motions determine the flow on an irregular grid which is then interpolated to derive quantities such as horizontal divergence or vertical vorticity. Interpolation is therefore a crucial step since mesoscale structures have mainly been studied through divergences and vorticities. We conclude that a reliable algorithm should be based on the tracking of coherent structures, like granules, since they are representative of the fluid motion, and should contain an interpolator which keeps track of the errors introduced either by location of the data (the shape of the irregular grid) or by the noise in the data.
Malherbe Jean-Marie
Rieutord Michel
Roudier Th.
Vigneau Jean
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