Authors: Dominic Payne (University of Michigan), Mojtaba Akhavan-Tafti (University of Michigan)

Using data from Parker Solar Probe encounters 13-23, we analyze the statistics of switchbacks and solar wind data from the outer corona to the young solar wind.  First, we analyze switchback variability with radial distance and Alfvén Mach number (Ma), and their associated velocity deflection and radial energy flux characteristics.  Although some switchbacks are observed below the Alfvén surface, they tend to be relatively close to Ma=1 and are much less common than switchback observations in the super-Alfvénic solar wind.  We identify a ‘conversion layer’ spanning Ma ~ 0.6-1.6 where deflection characteristics go through a transition and start to exceed 90 degrees in deflection angle.  Next, we examine the radial profiles of proton temperature anisotropies between 10 and 50 R_s to investigate how instabilities drive the thermodynamic evolution of switchbacks relative to the solar wind in the inner heliosphere. Switchback and solar wind anisotropies are mostly constrained by the oblique firehose and ion cyclotron instabilities.  At short distances (R ~ 10-30 R_s), these distributions tend to exhibit perpendicular-dominant anisotropies close to and sometimes beyond the ion cyclotron instability, but become more isotropic and eventually parallel-dominant with increasing radial distance until the parallel and oblique firehose instabilities constrain expansion-driven effects.  We find evidence that in the R~10-30 R_s range, the solar wind (especially fast wind) expansion exhibits significant non-adiabatic trends due to the high Alfvénicity.  By R~50 R_s, the distributions more closely resemble Chew-Goldberger-Low (CGL) adiabatic expansion.