Conservation of open solar magnetic flux and the floor in the heliospheric magnetic field

The near-Earth heliospheric magnetic field intensity, \B\, exhibits a strong solar sycle variation, but returens to the same floor value each solar minimum. The current minimum, however, has seen \B\ drop below previous minima, bringing in to question the existence of a floor, or at the very least requiring a re-assessment of its value. In this study we assume heliospheric flux consists of a constant open flux component and a time-varying contribution from CMEs. In this scenario, the true floor is \B\ withh zero CME contribution. Using observed CME rates over the solar cycle, we estimate the no-CME \B\ floor at similar to 4.o+/-0.3 nT, lower than previous floor estimates and below \B\ observed this solar minimum. We speculate that the drop in \B\ observed this minimum may be due to a persistently lower CME rate than the previous minimum, though there are large uncertainties in the supporting observational data. Citation: Owens, M.J., N.U. Crooker, N.A.Schwadron, T.S. Horbury, S. Yashiro, H. Xie, O.C. St. Cyr, and N. Gopalswamy (2008), conservation of open solar magnetic flux and the floor in the heliospheric magnetic field, Geophys. Res. Lett., 35, L20108, doi: 10.1029/2008GL035813.