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One of the striking observations from the Parker Solar Probe (PSP) spacecraftis the prevalence in the inner heliosphere of large amplitude, Alfv\'enicmagnetic field reversals termed 'switchbacks'. These $\delta B_R/B \sim\mathcal{O}(1$) fluctuations occur on a range of timescales and in {\empatches} separated by intervals of quiet, radial magnetic field. We usemeasurements from PSP to demonstrate that patches of switchbacks are localizedwithin the extensions of plasma structures originating at the base of thecorona. These structures are characterized by an increase in alpha particleabundance, Mach number, plasma $\beta$ and pressure, and by depletions in themagnetic field magnitude and electron temperature. These intervals are inpressure-balance, implying stationary spatial structure, and the fielddepressions are consistent with overexpanded flux tubes. The structures areasymmetric in Carrington longitude with a steeper leading edge and a small($\sim$1$^\circ$) edge of hotter plasma and enhanced magnetic fieldfluctuations. Some structures contain suprathermal ions to $\sim$85 keV that weargue are the energetic tail of the solar wind alpha population. The structuresare separated in longitude by angular scales associated with supergranulation.This suggests that these switchbacks originate near the leading edge of thediverging magnetic field funnels associated with the network magnetic field -the primary wind sources. We propose an origin of the magnetic fieldswitchbacks, hot plasma and suprathermals, alpha particles in interchangereconnection events just above the solar transition region and our measurementsrepresent the extended regions of a turbulent outflow exhaust.

A solar source of Alfv\'enic magnetic field switchbacks: {\em in situ} remnants of magnetic funnels on supergranulation scales