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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">Dear Loops friends,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">You might be interested in a paper that Manuel Luna and I recently submitted on "The Role of Asymmetries in Thermal Non-Equilibrium." It can be downloaded at
</span><a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__arxiv.org_abs_1905.09767&d=DwIBaQ&c=ApwzowJNAKKw3xye91w7BE1XMRKi2LN9kiMk5Csz9Zk&r=t_bIXD1NorvbdQ80J9NckbiYhjsNvSG0NiGAllxpmG0&m=fO7orLgMSDCaG2vc_1mTC4KrleYHNLuOX2vHY9hqfXw&s=MarJfF6HwumNITBOhMZl2236BOMBQlxMssIO2LQFtPo&e">https://urldefense.proofpoint.com/v2/url?u=http-3A__arxiv.org_abs_1905.09767&d=DwIBaQ&c=ApwzowJNAKKw3xye91w7BE1XMRKi2LN9kiMk5Csz9Zk&r=t_bIXD1NorvbdQ80J9NckbiYhjsNvSG0NiGAllxpmG0&m=fO7orLgMSDCaG2vc_1mTC4KrleYHNLuOX2vHY9hqfXw&s=MarJfF6HwumNITBOhMZl2236BOMBQlxMssIO2LQFtPo&e</a><span style="font-family:"Arial",sans-serif"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">I look forward to discussing any questions or comments you may have at the Loops Workshop in a couple weeks.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">Jim<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">ABSTRACT<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-align:justify;line-height:115%"><span style="font-family:"Arial",sans-serif"> Thermal non-equilibrium (TNE) is a fascinating situation that occurs in coronal magnetic flux tubes (loops) for which no solution to the
steady-state fluid equations exists. The plasma is constantly evolving even though the heating that produces the hot temperatures does not. This is the likely explanation of isolated phenomena such as prominences, coronal rain, and long-period pulsating loops,
but it may also have much broader relevance. As known for some time, TNE requires that the heating be both (quasi) steady and concentrated at low coronal altitudes. Recent studies indicate that asymmetries are also important, with large enough asymmetries
in the heating and/or cross-sectional area resulting in steady flow rather than TNE. Using reasonable approximations, we have derived two formulae for quantifying the conditions necessary for TNE. As a rough rule of thumb, the ratio of apex to footpoint heating
must be less than about 0.1, and asymmetries must be less than about a factor of 3. The precise values are case dependent. We have tested our formulae with 1D hydrodynamic loop simulations and find a very acceptable agreement. These results are important for
developing physical insight about TNE and assessing how widespread it may be on the Sun.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">********************************************************************************<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">James A. Klimchuk<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">NASA Goddard Space Flight Center<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">Solar Physics Lab, Code 671<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">Bldg. 21, Rm. 158<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">Greenbelt, MD 20771<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">USA<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">Phone: 1-301-286-9060<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">Fax: 1-301-286-7194<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">E-mail: <a href="mailto:James.A.Klimchuk@nasa.gov"><span style="color:blue">James.A.Klimchuk@nasa.gov</span></a>
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">Homepage: <a href="http://science.gsfc.nasa.gov/sed/index.cfm?fuseAction=people.jumpBio&&iPhonebookId=15844">
<span style="color:windowtext;text-decoration:none">http://science.gsfc.nasa.gov/sed/bio/james.a.klimchuk</span></a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">No endorsement by NASA is implied for any correspondence related to my official role in professional organizations.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif"> <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">********************************************************************************<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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