SIGN SINGULARITY OF THE MAGNETIC HELICITY FROM IN-SITU SOLAR-WIND OBSERVATIONS

Some turbulent signed measures show a singularity related to extreme o scillations in sign, the scaling behavior of cancellations between pos itive and negative contributions being characterized by the cancellati on exponent kappa. 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 polarizatio n of fluctuations at small scales. We recover a statistical correlatio n between kappa and the bulk solar wind speed when any correlation has been found between kappa and the distance from the Sun. Even if the u sual models of magnetic fluctuations based on random phases are able t o reproduce (in a statistical sense) the gross features of helicity fl uctuations, they cannot reproduce the behavior of sign singularity.