Authors: Samuel T. Badman (Center for Astrophysics | Harvard & Smithsonian) , Stuart D. Bale (UC Berkeley), Michael L. Stevens (Center for Astrophysics | Harvard & Smithsonian)

The solar alfvén surface is the boundary at which the solar wind bulk velocity exceeds the local alfvén speed and is a key parameter describing the atmosphere of the Sun and other stars. We study its structure and temporal evolution over the first half of solar cycle 25, using in situ data from Parker Solar Probe and Solar Orbiter and performing radial scaling. We construct large scale cuts of its topology over broad regions of longitude, associating features with solar wind sources. By performing the scaling with multiple spacecraft we test for the robustness of the features with respect to time evolution. Lastly, we determine the average height over half a solar cycle and compare with previous work.