Comparison of helicity signs in magnetic clouds and their solar source regions

Magnetic helicity, which is known as one of the few quantities that are conserved, quantifies the signed amount of twists, kinks, and inter-linkages of the magnetic field lines in a given magnetic field system. CMEs are one of the means by which the Sun ejects magnetic helicity into interplanetary space, and magnetic clouds (MCs) detected near the Earth may carry a similar amount of helicity ejected from solar source regions. If the helicity ejected by solar eruptions is conserved from the Sun to the Earth, we can assume that flux ropes in MCs should have similar characteristics with those in their solar source regions, and it is also expected that the signs of their helicties on the Sun and near the Earth should be same. With this expectation, we selected 36 CMEs that occurred at solar disk center among well identified 59 CME-MC pairs in the CDAW list, and determined the helicity signs in magnetic clouds and their solar source regions, respectively. The helicity signs in the solar source regions are determined by the amount of helicity injection through their photospheric surfaces using SOHO/MDI magnetograms, and the helicity signs in the MCs are estimated by adopting cylinder and torus models to ACE solar wind data. As a results, we found that among the total of 36 events, there are 30 helicity sign-consistent events (83%) and 6 sign-inconsistent events (17%). This result shows that most flux ropes erupted from the surface maintain their helicity signs from the Sun to the Earth, and supports that flux ropes in the MCs have a similar characteristic with those in their solar source regions. For 6 exceptional events, we investigate them in detail if they do not follow the helicity conservation rule or if they are come from the followings: (1) the helicity sign difference between the entire source active region and the local CME-originated region, (2) the wrong estimation of MC helicity signs by the fitting models, or (3) the uncertainty of helicity sign determination in the source region due to pre-existing opposite-sign helicity in a coronal volume of the source region. In this talk, we will show that our results support the idea of the helicity conservation rule of CDAW CME-MC pairs.