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Solar Wind Heating Near the Sun: A Radial Evolution Approach
Preprint   Open access

Solar Wind Heating Near the Sun: A Radial Evolution Approach

Yogesh, Leon Ofman, Kristopher Klein, Niranjana Shankarappa, Mihailo M Martinović, Gregory G Howes, Parisa Mostafavi, Scott A Boardsen, Viacheslav M Sadykov, Sanchita Pal, …
ArXiv.org
Cornell University
02/18/2026
DOI: 10.48550/arxiv.2602.10275
url
https://doi.org/10.48550/arxiv.2602.10275View
Preprint (Author's original)This preprint has not been evaluated by subject experts through peer review. Preprints may undergo extensive changes and/or become peer-reviewed journal articles. Open Access

Abstract

Characterizing the plasma state in the near-Sun environment is essential to constrain the mechanisms that heat and accelerate the solar wind. In this study, we use Parker Solar Probe (PSP) observations from Encounters 1 through 24 to investigate the radial evolution of solar wind plasma and magnetic field properties in this region. Using intervals with high field-of-view ( >85% ) coverage, we derive the radial profiles of magnetic field strength ( |B| ), proton density ( N ), bulk speed ( V ), total proton temperature ( T ), parallel ( T_(∥) ) and perpendicular ( T_(⊥) ) temperatures, temperature anisotropy ( T_(⊥)/T_(∥) ), plasma beta ( β ), Alfvén Mach number ( M_(A) ), and magnetic field fluctuations ( δB/B ) for sub and super-Alfvénic regions. In super-Alfvénic regions, power-law of|B| ,N ,V , andTas a function of heliocentric distance are broadly consistent with previous Helios results at>0.3AU. The radial evolution of the components of the temperature tensor reveals distinct behavior:T_(⊥)decreases monotonically with distance, whereasT_(∥)exhibits a non-monotonic trend – decreasing in the sub-Alfvénic region, increasing just beyond the Alfvén surface. We interpret the increase inT_(∥)as a proxy for proton beam occurrence. We further examine the evolution of magnetic field fluctuations, finding decreasing radial/parallel fluctuations but enhanced tangential/normal/perpendicular fluctuations in sunward direction. These fluctuations may provide free energy for beam generation and particle heating via wave-particle interactions.
 Physics - Solar and Stellar Astrophysics Physics - Space Physics

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