<p>First, I have provided some background on these phenomena at: <a href="https://astronomy.stackexchange.com/a/16786/13663">https://astronomy.stackexchange.com/a/16786/13663</a></p>
<p><a href="https://en.wikipedia.org/wiki/Solar_flare" rel="noreferrer">Solar flares</a> and <a href="https://en.wikipedia.org/wiki/Coronal_mass_ejection" rel="noreferrer">coronal mass ejections (CMEs)</a> are not the same phenomena.</p>
<blockquote>
<p>I am aware that radiation from these solar events does not travel directly outward from the direction of the sun but follows magnetic lines of force and may be subject to eddies and other other effects that modify the direction of travel.</p>
</blockquote>
<p>To what are you referring here?  The only things that follows the magnetic field are charged particles.  CMEs are huge blobs of <a href="https://en.wikipedia.org/wiki/Plasma_(physics)" rel="noreferrer">plasma</a> (i.e., ionized gas) that erupt from the sun and carry with them large deviations in the magnetic field.  Both solar flares and CMEs can generate what are called <a href="https://en.wikipedia.org/wiki/Solar_energetic_particles" rel="noreferrer">solar energetic particle (SEP)</a> events.  CMEs can also generate something called an energetic storm particle (ESP) event.  The distinction is the latter is an in situ inhancement of energetic particles that were generated by the shock ahead of the CME.  The former can be generated near the Sun.</p>
<p>Solar flares are primarily distinguished by their localized enhancement of UV and x-ray light, neither of which cares about the magnetic field.  Electromagnetic radiation propagates through space in the direction it was emitted and only really curves under extreme conditions (e.g., huge gravitational fields or extreme electromagnetic fields like those near a pulsar).</p>
<blockquote>
<p>What does the graph of average radiation intensity v radial distribution look like for a point in deep space (radiation intensity v degrees bearing from the line of maximum intensity) for a passing solar flare or CME?</p>
</blockquote>
<p>This depends upon what you mean by radiation.  If you are asking about charged particles, then it also depends upon the event.  Some CMEs &quot;sweep up&quot; and energize particles as they propagate so the intensity levels can actually increase with radial distance from the Sun out to varying distances (depending on CME strength etc.) then it will begin to decrease.  So the answer is that it's very complicated and it depends upon the specific event.  However, inside Mercury's orbit, the intensity levels of suprathermal particles (i.e., particles with kinetic energies &gt;100 eV for electrons, &gt;5 keV for protons) are higher, on average, than those near Earth.</p>
<p>For the electromagnetic radiation, that just decreases inversely squared with increasing distance from the source, as you would expect.</p>

CC BY-SA 4.0
2021-09-02T18:13:32.077Z
Thanks for that. It helps my understanding of the problem. I was asking from the perspective of crewed space flight to discover to what extent a shield on one side of the ship would protect the crew if pointed at the Sun.
Slarty
CC BY-SA 4.0
2021-08-31T14:23:14.080Z
2021-08-31T14:23:14.080Z
honeste_vivere
<p>I have just found this paper which seems very relevant:</p>
<p><a href="https://www.sciencedirect.com/science/article/abs/pii/S1350448799000633?via%3Dihub" rel="nofollow noreferrer">https://www.sciencedirect.com/science/article/abs/pii/S1350448799000633?via%3Dihub</a></p>
<p>&quot;Particles arising at some remote location from the sun are diffusing through the interplanetary media and show some anisotropy in that the back scattered particles are absent on the leading edge of the expanding radiation field. Following the first tens of minutes after initial particle arrival, isotropy is usually achieved. We will henceforth assume the radiation fields incident on the spacecraft to be isotropic.&quot;</p>
<p>It would appear that except for a fairly brief initial period that radiation will be isotropic.</p>

CC BY-SA 4.0
2023-11-15T17:14:06.633Z
2023-11-15T17:14:06.633Z
Slarty
<p>I have read a number of articles about Coronal Mass Ejections (CME) and solar flares and I’m trying to establish how directional the radiation from them is.</p>
<p>I am aware that radiation from these solar events does not travel directly outward from the direction of the sun but follows magnetic lines of force and may be subject to eddies and other other effects that modify the direction of travel.</p>
<p>So my question is: <strong>What does the graph of average radiation intensity v radial distribution look like for a point in deep space</strong> (radiation intensity v degrees bearing from the line of maximum intensity) <strong>for a passing solar flare or CME?</strong> For the purpose of this question, deep Space is the region between the orbits of Venus and Mars</p>
<p><strong>Edit</strong></p>
<p>For the purposes of this question &quot;radiation&quot; refers to particulate radiation such as electrons, heavy nuclei and especially protons originating from the Sun during a solar flare or CME (peak flux in Watts per square metre).</p>
<p>In case that an exact answer is not available an approximate answer would be acceptable.</p>

CC BY-SA 4.0
2021-05-31T07:37:15.163Z
Radiation *does* travel outward radially and does not follow magnetic field lines. The ejected mass (protons and alpha particles mostly) does follow the interplanetary magnetic field (sometimes confusingly called particle radiation... maybe that's where some of the confusion comes from)
planetmaker
CC BY-SA 4.0
2021-05-31T07:55:31.857Z
@planetmaker thank you for that clarification. By radiation I meant the proton and particle radiation which I believe are the more significant part
Slarty
CC BY-SA 4.0
2021-05-31T08:15:46.667Z
@Slarty the main point really is when talking of particles, use clear and unambiguous terms like "particle flux", "particle density", "velocity distribution", "momentum distribution", "kinetic energy distribution" etc - radiation is a word which is commonly only associated with electromagnetic radiation. And especially "radiation intensity": what do you really mean with that? Which of the aforementioned words? Or another even?
planetmaker
CC BY-SA 4.0
2021-05-31T14:00:02.123Z
Yes good point I could have been clearer. Unfortunately I'm not fully informed about this area. As an aside I think alpha and beta radiation are in common usage.
Slarty
CC BY-SA 4.0
2021-06-01T11:14:55.543Z
Since there have been no answers yet and my original question was not clear. I have edited it to define radiation as particulate rather than electromagnetic.
Slarty
CC BY-SA 4.0
2021-06-04T00:07:16.577Z
If an answer isn't forthcoming here, there is the possibility of moving it to Space SE. The problem is that it's not off-topic here so it is hard to close it. For questions that are too old to migrate (90+ days) it is easier to re-ask a similar question in a new site, but for a new question like this, moving would either be possible by asking a moderator about it through flagging or through meta, or by self-deleting here and re-posting there. Using a moderator's assistance is preferable and avoids the possibility of the question being re-opened here at a later time.
uhoh
CC BY-SA 4.0
2021-06-04T17:07:19.630Z
Perhaps I will give it a month and then see about moving it...
Slarty
CC BY-SA 4.0
2021-05-26T06:09:22.373Z
This is an interesting question! There are both charged and neutral particles which may travel differently. While a snapshot of the pattern of the ejected material in space looks like a spiral (think rotating lawn sprinkler), I think the trajectories of the particles themselves is still *mostly* radial plus some turbulence and temperature. But let's see how wrong I turn out to be :-)
uhoh
<radiation><solar-flare><coronal-mass-ejection><particles>
Directionality of solar flares
Slarty
# Directionality of solar flares

(Asked by: username_0 on 2021-05-26)

I have read a number of articles about Coronal Mass Ejections (CME) and solar flares and I’m trying to establish how directional the radiation from them is.

I am aware that radiation from these solar events does not travel directly outward from the direction of the sun but follows magnetic lines of force and may be subject to eddies and other other effects that modify the direction of travel.

So my question is: **What does the graph of average radiation intensity v radial distribution look like for a point in deep space** (radiation intensity v degrees bearing from the line of maximum intensity) **for a passing solar flare or CME?** For the purpose of this question, deep Space is the region between the orbits of Venus and Mars

**Edit**

For the purposes of this question "radiation" refers to particulate radiation such as electrons, heavy nuclei and especially protons originating from the Sun during a solar flare or CME (peak flux in Watts per square metre).

In case that an exact answer is not available an approximate answer would be acceptable.

**Tags:** radiation, solar-flare, coronal-mass-ejection, particles
> **Comments:**
> **username_2**: This is an interesting question! There are both charged and neutral particles which may travel differently. While a snapshot of the pattern of the ejected material in space looks like a spiral (think rotating lawn sprinkler), I think the trajectories of the particles themselves is still *mostly* radial plus some turbulence and temperature. But let's see how wrong I turn out to be :-)  
> **username_1**: Radiation *does* travel outward radially and does not follow magnetic field lines. The ejected mass (protons and alpha particles mostly) does follow the interplanetary magnetic field (sometimes confusingly called particle radiation... maybe that's where some of the confusion comes from)  
> **username_0**: @planetmaker thank you for that clarification. By radiation I meant the proton and particle radiation which I believe are the more significant part  
> **username_1**: @Slarty the main point really is when talking of particles, use clear and unambiguous terms like "particle flux", "particle density", "velocity distribution", "momentum distribution", "kinetic energy distribution" etc - radiation is a word which is commonly only associated with electromagnetic radiation. And especially "radiation intensity": what do you really mean with that? Which of the aforementioned words? Or another even?  
> **username_0**: Yes good point I could have been clearer. Unfortunately I'm not fully informed about this area. As an aside I think alpha and beta radiation are in common usage.  
> **username_0**: Since there have been no answers yet and my original question was not clear. I have edited it to define radiation as particulate rather than electromagnetic.  
> **username_2**: If an answer isn't forthcoming here, there is the possibility of moving it to Space SE. The problem is that it's not off-topic here so it is hard to close it. For questions that are too old to migrate (90+ days) it is easier to re-ask a similar question in a new site, but for a new question like this, moving would either be possible by asking a moderator about it through flagging or through meta, or by self-deleting here and re-posting there. Using a moderator's assistance is preferable and avoids the possibility of the question being re-opened here at a later time.  
> **username_0**: Perhaps I will give it a month and then see about moving it...  

---

## 2 answers

### Answer by username_3 on 2021-08-31. Score: 5

First, I have provided some background on these phenomena at: <https://astronomy.stackexchange.com/a/16786/13663>

[Solar flares](https://en.wikipedia.org/wiki/Solar_flare) and [coronal mass ejections (CMEs)](https://en.wikipedia.org/wiki/Coronal_mass_ejection) are not the same phenomena.

> I am aware that radiation from these solar events does not travel directly outward from the direction of the sun but follows magnetic lines of force and may be subject to eddies and other other effects that modify the direction of travel.

To what are you referring here? The only things that follows the magnetic field are charged particles. CMEs are huge blobs of [plasma](https://en.wikipedia.org/wiki/Plasma_(physics)) (i.e., ionized gas) that erupt from the sun and carry with them large deviations in the magnetic field. Both solar flares and CMEs can generate what are called [solar energetic particle (SEP)](https://en.wikipedia.org/wiki/Solar_energetic_particles) events. CMEs can also generate something called an energetic storm particle (ESP) event. The distinction is the latter is an in situ inhancement of energetic particles that were generated by the shock ahead of the CME. The former can be generated near the Sun.

Solar flares are primarily distinguished by their localized enhancement of UV and x-ray light, neither of which cares about the magnetic field. Electromagnetic radiation propagates through space in the direction it was emitted and only really curves under extreme conditions (e.g., huge gravitational fields or extreme electromagnetic fields like those near a pulsar).

> What does the graph of average radiation intensity v radial distribution look like for a point in deep space (radiation intensity v degrees bearing from the line of maximum intensity) for a passing solar flare or CME?

This depends upon what you mean by radiation. If you are asking about charged particles, then it also depends upon the event. Some CMEs "sweep up" and energize particles as they propagate so the intensity levels can actually increase with radial distance from the Sun out to varying distances (depending on CME strength etc.) then it will begin to decrease. So the answer is that it's very complicated and it depends upon the specific event. However, inside Mercury's orbit, the intensity levels of suprathermal particles (i.e., particles with kinetic energies >100 eV for electrons, >5 keV for protons) are higher, on average, than those near Earth.

For the electromagnetic radiation, that just decreases inversely squared with increasing distance from the source, as you would expect.

> **Comments:**
> **username_0**: Thanks for that. It helps my understanding of the problem. I was asking from the perspective of crewed space flight to discover to what extent a shield on one side of the ship would protect the crew if pointed at the Sun.  

---

### Answer by username_0 on 2023-11-15. Score: 1

I have just found this paper which seems very relevant:

<https://www.sciencedirect.com/science/article/abs/pii/S1350448799000633?via%3Dihub>

"Particles arising at some remote location from the sun are diffusing through the interplanetary media and show some anisotropy in that the back scattered particles are absent on the leading edge of the expanding radiation field. Following the first tens of minutes after initial particle arrival, isotropy is usually achieved. We will henceforth assume the radiation fields incident on the spacecraft to be isotropic."

It would appear that except for a fairly brief initial period that radiation will be isotropic.


---

