Analysing the Effects of Apodizing Windows on Local Correlation Tracking Using Nirvana Simulations of Convection

作者：Louis Rohan E^*; Ravindra B; Georgoulis Manolis K; Kueker Manfred

来源：Solar Physics, 2015, 290(4): 1135-1146.

DOI：10.1007/s11207-015-0659-2

• Velocity fields
• Photosphere

We employ different shapes of apodizing windows in the local correlation tracking (LCT) routine to retrieve horizontal velocities using numerical simulations of convection. LCT was applied on a time sequence of temperature maps generated by the Nirvana code with four different apodizing windows, Gaussian, Lorentzian, trapezoidal, and triangular, with varying widths. In terms of correlations (between the LCT-retrieved and simulated flow field), the triangular and the trapezoidal perform the best and worst, respectively. By segregating the intrinsic velocities in the simulations on the basis of their magnitudes, we find that for all windows a significantly higher correlation is obtained for the intermediate and high-velocity bins and only modest or weak values in the low-velocity bins. The differences between the LCT-retrieved and simulated flow fields were determined spatially. They show large residuals at or close to the boundary of granules. The extent to which the horizontal flow vectors retrieved by LCT are similar to the simulated values entirely depends on the width of the central peak of the apodizing window for a given sigma. Even though LCT suffers from a lack of spatial content, as seen in simulations, its simplicity and speed could serve as a viable first-order tool to probe horizontal flows. This would be an ideal tool for large data sets.

• 出版日期2015-4