.[1] A recent two-dimensional (radial distance r and solar longitude f) model for the solar wind is driven using 1-hour average data from the Wind spacecraft. We extend the treatment of the Sun's magnetic field to allow a nonzero azimuthal component B f at the source surface, assumed to be at the photosphere where r = R s , in addition to the radial component B r . We find nonzero azimuthal magnetic fields at the source surface with important consequences for the more distant heliosphere. The averages jB f (R s )j and jB r (R s )j inferred over solar cycle 23 are 0.44 AE 0.48 mT (4.4 AE 4.8 mG) and 120 AE 30 mT (1.2 AE 0.3 G) at the photosphere, respectively. Both components vary with time by more than an order of magnitude, with jB f (R s )j ≤ jB r (R s )j. While the surface magnetic field is closely radial on average it is sometimes 20°from radial. Both B f and B r vary smoothly on periods of 10 hours, with evidence for relatively narrow current sheets, and vary with the solar cycle: B r (R s ) is correlated with the sunspot number, but with a time lag of 20 months, while B f (R s ) has a two level behavior, decreasing near solar maximum and increasing near solar minimum. Our results and model can account naturally for non-Parker-like magnetic field directions at 1 AU since the B f fields inferred at the source surface lead to the B f and B r fields at 1 AU having similar average magnitudes and large variability.Citation: Schulte in den Bäumen, H., I. H. Cairns, and P. A. Robinson (2011), Modeling 1 AU solar wind observations to estimate azimuthal magnetic fields at the solar source surface, Geophys.