Authors: Zilei Chen (Florida Institute of Technology), Sofiane Bourouaine (Florida Institute of Technology), Jean C. Perez (Florida Institute of Technology)

The Parker Solar Probe spacecraft has provided data from multiple near-Sun encounters and, during recent encounters, in situ measurements of sub-Alfvénic regions. Analyses of solar wind in these sub-Alfvénic regions show strong alignment between magnetic and velocity field vectors. However, little is known about the behavior of residual energy in these regions. We present an analysis of residual energy spectra from 121 one-hour sub-Alfvénic intervals observed during PSP Encounter 22, the spacecraft’s first closest approach to the Sun at 9.86 R☉. Preliminary results show a concentration of sub-Alfvénic intervals near perihelion, with residual energy spectral indices close to −3/2, in contrast to the index of approximately −2 observed at 1 AU. These results indicate shallower residual energy spectra in sub-Alfvénic regions compared to super-Alfvénic regions and support the observed similarity between magnetic field and velocity fluctuations in sub-Alfvénic solar wind.