Sign singularity of the magnetic helicity from in situ solar wind observations

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 cancel- lation exponent i. Using in situ observations of magnetic Ñuctuations 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 Ñuctuations at small scales. We recover a statistical correlation between i and the bulk solar wind speed when any correlation has been found between i and the distance from the Sun. Even if the usual models of magnetic Ñuctuations based on random phases are able to reproduce (in a statistical sense) the gross features of helicity Ñuctuations, they cannot reproduce the behavior of sign singularity.