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rice-solar-physics / ebtelplusplus

An implementation of the enthalpy-based thermal evolution of loops (EBTEL) model implemented in C++ and wrapped in Python
https://ebtelplusplus.readthedocs.io
GNU General Public License v3.0
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Free-free emission in radiative losses? #83

Closed jwreep closed 6 months ago

jwreep commented 10 months ago

The code has this comment:

// NOTE: free-free radiation is included in the parameter values for log_10 T > 7.63

Is f-f radiation not included at lower temperatures in the power law fit? If so, why? It should be non-negligible down to much lower temperatures.

wtbarnes commented 10 months ago

Good point. I copied the power-law radiative loss function straight from HYDRAD which also includes this comment: https://github.com/rice-solar-physics/HYDRAD/blob/0fa1f9949540e6b9379548c72a030621fdee381d/Radiation_Model/source/radiation.cpp#L712 so I would pass that question on to @sjbradshaw.

My assumption was that the continuum is included in that power-law approximation everywhere but that it dominates at $\log{T}>7.63$. Here's a plot that shows a comparison between the RK loss (the one used here) and the radiative losses from CHIANTI that include the continuum contribution:

image

Naively, it appears that the component > 7.63 is specifically constructed to mimic the dominant continuum component at those high temperatures.

sjbradshaw commented 10 months ago

The power-law radiation function in HYDRAD includes the free-free (continuum) emission at the highest temperatures (> log T = 7.63). So, this will also be what is used in EBTEL++.

[FYI: The HYDRAD radiation code also includes a separate function to calculate just the free-free emission, which is added to the line emission calculated ion-by-ion for (e.g.) non-equilibrium radiation, in the appropriate temperature range.]

Hope this helps.

Cheers,

Steve

From: Will Barnes @.> Sent: Tuesday, December 19, 2023 8:28 PM To: rice-solar-physics/ebtelPlusPlus @.> Cc: sjbradshaw @.>; Mention @.> Subject: Re: [rice-solar-physics/ebtelPlusPlus] Free-free emission in radiative losses? (Issue #83)

Good point. I copied the power-law radiative loss function straight from HYDRAD which also includes this comment: https://github.com/rice-solar-physics/HYDRAD/blob/0fa1f9949540e6b9379548c72a030621fdee381d/Radiation_Model/source/radiation.cpp#L712 https://urldefense.com/v3/__https:/github.com/rice-solar-physics/HYDRAD/blob/0fa1f9949540e6b9379548c72a030621fdee381d/Radiation_Model/source/radiation.cpp*L712__;Iw!!BuQPrrmRaQ!jaC70dJJYEChJWaEy99PTlACBmZ0wjTBHY3-zQi0vUX4GmCdeD12VNajGDjFZF0wFSJPu68m_tdYjNN12GHXQ77BOALhnfKGwiE$ so I would pass that question on to @sjbradshaw https://urldefense.com/v3/__https:/github.com/sjbradshaw__;!!BuQPrrmRaQ!jaC70dJJYEChJWaEy99PTlACBmZ0wjTBHY3-zQi0vUX4GmCdeD12VNajGDjFZF0wFSJPu68m_tdYjNN12GHXQ77BOALh_QfL-zA$ .

My assumption was that the continuum is included in that power-law approximation everywhere but that it dominates at $\log{T}>7.63$. Here's a plot that shows a comparison between the RK loss (the one used here) and the radiative losses from CHIANTI that include the continuum contribution:

image.png (view on web) https://urldefense.com/v3/__https:/github.com/rice-solar-physics/ebtelPlusPlus/assets/8676141/da17183e-cffc-4bc6-b4a9-3c25e1426e1c__;!!BuQPrrmRaQ!jaC70dJJYEChJWaEy99PTlACBmZ0wjTBHY3-zQi0vUX4GmCdeD12VNajGDjFZF0wFSJPu68m_tdYjNN12GHXQ77BOALhwrqe7NQ$

Naively, it appears that the component > 7.63 is specifically constructed to mimic the dominant continuum component at those high temperatures.

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jwreep commented 10 months ago

Does that mean HYDRAD neglects free-free for lower temperatures when using power law losses?

sjbradshaw commented 10 months ago

The power-law losses are just a fit to a (presumably) fairly detailed calculation of radiative losses. So, if those original calculations included free-free at lower temperatures then the power-law losses will too; if not, then no.

From: Jeffrey Reep @.> Sent: Wednesday, December 20, 2023 6:47 PM To: rice-solar-physics/ebtelPlusPlus @.> Cc: sjbradshaw @.>; Mention @.> Subject: Re: [rice-solar-physics/ebtelPlusPlus] Free-free emission in radiative losses? (Issue #83)

Does that mean HYDRAD neglects free-free for lower temperatures when using power law losses?

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wtbarnes commented 6 months ago

I'm going to close this because at the very least, I think this is out of scope for ebtel++. Feel free to reopen if you think there are still questions that need to be answered.