Solar cycle–dependent helicity transport by magnetic clouds

[1] Magnetic clouds observed with the Wind and ACE spacecraft are fit with the static, linear force-free cylinder model to obtain estimates of the chirality, fluxes, and magnetic helicity of each event. The fastest magnetic clouds (MCs) are shown to carry the most flux and helicity. We calculate the net cumulative helicity which measures the difference in rightand left-handed helicity contained in MCs over time. The net cumulative helicity does not average to zero; rather, a strong left-handed helicity bias develops over the solar cycle, dominated by the largest events of cycle 23: Bastille Day 2000 and 28 October 2003. The majority of MCs (‘‘slow’’ events, hVri < 500 km/s) have a net cumulative helicity profile that appears to be modulated by the solar activity cycle. This is far less evident for ‘‘fast’’ MC events (hVri 500 km/s), which were disproportionately left-handed over our data set. A brief discussion about the various solar sources of CME helicity and their implication for dynamo processes is included.