  Smoothing methods and SiZer (SIgnificant ZERo crossing of the derivatives)
are useful tools for exploring significant underlying structures in data
samples. An extension of SiZer to circular data, namely CircSiZer, is
introduced. Based on scale-space ideas, CircSiZer presents a graphical device
to assess which observed features are statistically significant, both for
density and regression analysis with circular data. The method is intended for
analyzing the behavior of wind direction in the atlantic coast of Galicia (NW
Spain) and how it has an influence over wind speed. The performance of
CircSiZer is also checked with some simulated examples.
