The diagnostic temperature discrepancy as evidence for non-Maxwellian coronal electrons
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arXiv
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| Natura: | Preprint |
| Pubblicazione: |
2026
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| _version_ | 1866914501375295488 |
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| author | Edmonds, Victor |
| author_facet | Edmonds, Victor |
| contents | Two independent electron temperature diagnostics applied to the quiet solar corona yield systematically different results. Radio brightness temperatures from the Nancay Radioheliograph indicate T_e ~ 0.6 MK, while hydrostatic scale-height modeling requires T_e ~ 1.5 MK. Both probe electrons; they disagree by a factor of R = 2.4 +/- 0.3. This discrepancy persists across eight years spanning solar minimum and is confirmed by LOFAR at lower frequencies. We consider turbulent scattering, which suppresses brightness temperature, but comparison with the FORWARD/PSIMAS Maxwellian model shows the standard thermal structure predicts ~1.6 MK; scattering accounts for the reduction toward observed MWA values but not the gap to 620 kK. The ratio R is also cycle-invariant despite measured variations in turbulence. We propose the residual discrepancy reflects non-Maxwellian electron velocity distributions. Radio bremsstrahlung samples the distribution core; ionization and scale heights are dominated by the suprathermal tail. For kappa distributions, the predicted ratio kappa/(kappa - 3/2) matches R = 2.4 at kappa ~ 2-3, consistent with spectroscopic measurements in active regions but in tension with perturbative predictions of kappa ~ 10-25. We predict Active Region cores should show a collapsed ratio (R <= 1.5) as collisionality restores thermal equilibrium. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2603_10040 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | The diagnostic temperature discrepancy as evidence for non-Maxwellian coronal electrons Edmonds, Victor Solar and Stellar Astrophysics Plasma Physics Space Physics Two independent electron temperature diagnostics applied to the quiet solar corona yield systematically different results. Radio brightness temperatures from the Nancay Radioheliograph indicate T_e ~ 0.6 MK, while hydrostatic scale-height modeling requires T_e ~ 1.5 MK. Both probe electrons; they disagree by a factor of R = 2.4 +/- 0.3. This discrepancy persists across eight years spanning solar minimum and is confirmed by LOFAR at lower frequencies. We consider turbulent scattering, which suppresses brightness temperature, but comparison with the FORWARD/PSIMAS Maxwellian model shows the standard thermal structure predicts ~1.6 MK; scattering accounts for the reduction toward observed MWA values but not the gap to 620 kK. The ratio R is also cycle-invariant despite measured variations in turbulence. We propose the residual discrepancy reflects non-Maxwellian electron velocity distributions. Radio bremsstrahlung samples the distribution core; ionization and scale heights are dominated by the suprathermal tail. For kappa distributions, the predicted ratio kappa/(kappa - 3/2) matches R = 2.4 at kappa ~ 2-3, consistent with spectroscopic measurements in active regions but in tension with perturbative predictions of kappa ~ 10-25. We predict Active Region cores should show a collapsed ratio (R <= 1.5) as collisionality restores thermal equilibrium. |
| title | The diagnostic temperature discrepancy as evidence for non-Maxwellian coronal electrons |
| topic | Solar and Stellar Astrophysics Plasma Physics Space Physics |
| url | https://arxiv.org/abs/2603.10040 |