Comment on “What causes the flux excess in the heliospheric magnetic field?” by E. J. Smith

hereafter S11) advises against employing the modulus of the radial component of the interplanetary magnetic field (IMF) when using in situ magnetic field measurements from the heliosphere to remotely sense the open solar flux and argues that it causes what Lockwood et al. [2009aLockwood et al. [ , 2009b] ] (LEA09) have termed the "excess flux," as detected empirically by Owens et al.[2008] (OEA08).We here point out the wider implications of this debate about the best way to derive open solar flux (OSF) from measurements made by near-Earth spacecraft.The aim is to quantify OSF (also called the coronal source flux), and we here consider the "unsigned" OSF-i.e., the total magnetic flux (of either polarity) threading the coronal source surface (which is usually taken to be at a heliocentric sphere of radius R = 2.5R • , where R • is the mean photospheric radius).The approaches of S11 and OEA08/LEA09 are actually complementary, each with its own strengths and weaknesses.We therefore think it neither correct nor helpful to advocate the use of one over the other, rather, it is important to fully understand the strengths, limitations, and applicability of both.What is most interesting is that the two approaches generate similar answers in several important respects.We here concentrate on the implications for the long series of measurements made close to Earth (i.e., in the ecliptic plane near r = R 1 = 1 astronomical unit [AU]).