Reply to comment by H. Q. Feng, D. J. Wu, and J. K. Chao on “Comparison of small‐scale flux rope magnetic properties to large‐scale magnetic clouds: Evidence for reconnection across the HCS”?

Abstract

[1] The comment by Feng et al. [2010] suggests that the semi-automated algorithm developed by Cartwright and Moldwin [2008] is not always a reliable method of identifying flux ropes and that the duration distribution of flux ropes in the solar wind is not bimodal. The semi-automated method was developed in an attempt to remove the subjective nature of visual flux rope identification by using quantitative minimum criteria for flux rope selection. It searches for the classic signatures of a flux rope; that of a core field enhancement coincident with an inflection point in the bipolar field of the flux rope. The automated method identified 68 flux ropes of which Feng et al. [2010] find that 10 have magnetic field rotation signatures that are not smooth (low variance) and hence should not be considered flux ropes. It is possible that a small percentage of the events found by the semi-automated program were random IMF fluctuations rather than flux ropes. The smoothness (or low variance) of the flux rope rotation signature can depend on the presence of waves [e.g., Moldwin and Hughes, 1992] and has been included as one of the several identifying properties of magnetic clouds [e.g., Burlaga et al., 1981]. How low variance or smooth a flux rope can be is subjective from survey to survey, but was not one of the selection criterions for the automated survey. To examine if the inclusion of the non-smooth events influences the conclusions of the Cartwright and Moldwin [2008] study, we removed the 10 flux ropes and analyzed the duration distribution of small to large-scale size flux ropes.