Sign Singularity of the Magnetic Helicity from in Situ Solar Wind Observations

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Abstract
Some turbulent signed measures show a singularity related to extreme oscillations in sign, the scaling behavior of cancellations between positive and negative contributions being characterized by the cancellation exponent κ. Using in situ observations of magnetic fluctuations in the solar wind, we show that magnetic helicity is sign singular, a property that underlies the dominance of a single sign of polarization of fluctuations at small scales. We recover a statistical correlation between κ and the bulk solar wind speed when any correlation has been found between κ and the distance from the Sun. Even if the usual models of magnetic fluctuations based on random phases are able to reproduce (in a statistical sense) the gross features of helicity fluctuations, they cannot reproduce the behavior of sign singularity.