https://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=The_Alfven_Speed_above_a_Sunspot,_and_Gamma-rays&feed=atom&action=historyThe Alfven Speed above a Sunspot, and Gamma-rays - Revision history2024-03-28T18:30:30ZRevision history for this page on the wikiMediaWiki 1.16.0https://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=The_Alfven_Speed_above_a_Sunspot,_and_Gamma-rays&diff=10699&oldid=prevSchriste at 16:51, 22 August 20182018-08-22T16:51:28Z<p></p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|title = The Alfv&eacute;n Speed above a Spot, and Gamma-rays </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|title = The Alfv&eacute;n Speed above a Spot, and Gamma-rays </div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>|number = <del class="diffchange diffchange-inline">148</del></div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>|number = <ins class="diffchange diffchange-inline">149</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|first_author = H. Hudson</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|first_author = H. Hudson</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|second_author = L. Fletcher </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|second_author = L. Fletcher </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|publish_date = 12 April 2011</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|publish_date = 12 April 2011</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>|next_nugget={{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::<del class="diffchange diffchange-inline">149</del>]]}}</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>|next_nugget={{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::<ins class="diffchange diffchange-inline">150</ins>]]}}</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>|previous_nugget={{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::<del class="diffchange diffchange-inline">147</del>]]}}</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>|previous_nugget={{#ask: [[Category:Nugget]] [[RHESSI Nugget Index::<ins class="diffchange diffchange-inline">148</ins>]]}}</div></td></tr>
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</table>Schristehttps://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=The_Alfven_Speed_above_a_Sunspot,_and_Gamma-rays&diff=10690&oldid=prevSchriste at 16:43, 22 August 20182018-08-22T16:43:53Z<p></p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|publish_date = 12 April 2011</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|publish_date = 12 April 2011</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>|next_nugget = [<del class="diffchange diffchange-inline">http</del>:<del class="diffchange diffchange-inline">//sprg.ssl.berkeley.edu/~tohban/wiki/index.php/Decimetric_pulsations_and_coronal_X-ray_sources Decimetric Pulsations and Coronal X-ray Sources</del>]</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>|next_nugget=<ins class="diffchange diffchange-inline">{{#ask: [</ins>[<ins class="diffchange diffchange-inline">Category</ins>:<ins class="diffchange diffchange-inline">Nugget</ins>]<ins class="diffchange diffchange-inline">] [[RHESSI Nugget Index::149]]}}</ins></div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>|previous_nugget = [[<del class="diffchange diffchange-inline">Slow Magnetoacoustic Waves in Two-Ribbon Flares</del>]]</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>|previous_nugget=<ins class="diffchange diffchange-inline">{{#ask: </ins>[[<ins class="diffchange diffchange-inline">Category:Nugget]] [[RHESSI Nugget Index::147</ins>]]<ins class="diffchange diffchange-inline">}}</ins></div></td></tr>
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</table>Schristehttps://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=The_Alfven_Speed_above_a_Sunspot,_and_Gamma-rays&diff=8789&oldid=prevHhudson: /* Theory */2015-12-30T21:08:05Z<p><span class="autocomment">Theory</span></p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>The theory behind the extrapolations in Figure 3 is very simple and safe,</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>The theory behind the extrapolations in Figure 3 is very simple and safe,</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>though.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>though.</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>For a spot like this we <del class="diffchange diffchange-inline">could expect </del>an Alfv&eacute;n speed of <del class="diffchange diffchange-inline">c/3 at 10</del>,<del class="diffchange diffchange-inline">000 km</del></div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>For a spot like this we <ins class="diffchange diffchange-inline">estimate </ins>an Alfv&eacute;n <ins class="diffchange diffchange-inline">speed, using the usual </ins></div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del class="diffchange diffchange-inline">altitude</del>.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">relationship, to exceed the </ins>speed of <ins class="diffchange diffchange-inline">light.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">Of course this is non-physical</ins>, <ins class="diffchange diffchange-inline">but it is strikingly different from the usual assumption about the </ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">Alfv&eacute;n speed. </ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">This is just what reasonable estimates of '''B''' and ''n'' lead to, and the result suggests that plasma processes</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">in the coronal regions of a sunspot must be treated relativistically</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>[[File:149f3.png|thumb|center|700px|'''Figure 3''': Three panels showing, as </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>[[File:149f3.png|thumb|center|700px|'''Figure 3''': Three panels showing, as </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>a function of height above the center of a major sunspot, the magnetic field,</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>a function of height above the center of a major sunspot, the magnetic field,</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>the Alfv&eacute;n speed, and the plasma beta.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>the Alfv&eacute;n speed <ins class="diffchange diffchange-inline">as estimated by the standard formula</ins>, and the plasma beta.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>The assumed parameters for the sunspot are a central field of 3500 G and</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>The assumed parameters for the sunspot are a central field of 3500 G and</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>an umbral radius of 10,000 km.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>an umbral radius of 10,000 km.</div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins style="color: red; font-weight: bold; text-decoration: none;">The dashed line shows the speed of light.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins style="color: red; font-weight: bold; text-decoration: none;">''Note added 30-December 2015: our thanks to Serge Koutchmy for noticing that the original version of this figure was grossly erroneous.''</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>]]</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>]]</div></td></tr>
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</table>Hhudsonhttps://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=The_Alfven_Speed_above_a_Sunspot,_and_Gamma-rays&diff=4339&oldid=prevHhudson: corrected infobox2011-04-16T17:20:19Z<p>corrected infobox</p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|second_author = L. Fletcher </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|second_author = L. Fletcher </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|publish_date = 12 April 2011</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|publish_date = 12 April 2011</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>|next_nugget = [<del class="diffchange diffchange-inline">[</del>Decimetric Pulsations and Coronal X-ray Sources<del class="diffchange diffchange-inline">]</del>]</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>|next_nugget = [<ins class="diffchange diffchange-inline">http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/Decimetric_pulsations_and_coronal_X-ray_sources </ins>Decimetric Pulsations and Coronal X-ray Sources]</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|previous_nugget = [[Slow Magnetoacoustic Waves in Two-Ribbon Flares]]</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|previous_nugget = [[Slow Magnetoacoustic Waves in Two-Ribbon Flares]]</div></td></tr>
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</table>Hhudsonhttps://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=The_Alfven_Speed_above_a_Sunspot,_and_Gamma-rays&diff=4318&oldid=prevHhudson: polishing...2011-04-12T14:27:03Z<p>polishing...</p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>illustrate the distinct lack of a gamma-ray signature.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>illustrate the distinct lack of a gamma-ray signature.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>RHESSI has shown that gamma-ray flares are quite different from ordinary</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>RHESSI has shown that gamma-ray flares are quite different from ordinary</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>flares, i.e. that <del class="diffchange diffchange-inline">Kahler's </del>"big flare syndrome" (where everything scales</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>flares, i.e. that <ins class="diffchange diffchange-inline">the </ins>"big flare syndrome" (where everything scales</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>together) does not apply in this case.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>together) does not apply in this case <ins class="diffchange diffchange-inline">- here we see a big flare, with a sunquake as well, and yet no gamma rays</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>For this flare, Figure 2 shows that there was negligible [http://en.wikipedia.org/wiki/Solar_surface_fusion 2.2 MeV gamma-ray emission line], RHESSI's most sensitive tool for this purpose, and </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>For this flare, Figure 2 shows that there was negligible [http://en.wikipedia.org/wiki/Solar_surface_fusion 2.2 MeV gamma-ray emission line], RHESSI's most sensitive tool for this purpose, and </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>that the hard X-ray spectrum was weak above 50 keV.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>that the hard X-ray spectrum was weak above 50 keV.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>[[File:149f2.png|thumb|center|400px|'''Figure 2''': Time series of counts at <del class="diffchange diffchange-inline">50-</del>100 keV (gold) and at 2200-2250 keV (red), the latter a crude indication of the presence or absence of gamma-rays. In this case, despite the X classification of the flare, there were no detectable gamma rays and only a weak <del class="diffchange diffchange-inline">50-100 keV </del>hard X-ray signature.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>[[File:149f2.png|thumb|center|400px|'''Figure 2''': Time series of counts at 100 <ins class="diffchange diffchange-inline">keV (blue), 200 </ins>keV (gold) and at 2200-2250 keV (red), the latter a crude indication of the presence or absence of gamma-rays. In this case, despite the X classification of the flare, there were no detectable gamma rays and only a weak hard X-ray signature <ins class="diffchange diffchange-inline">with a relatively steep spectrum</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>]]</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>]]</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>== Theory ==</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>== Theory ==</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>As the <del class="diffchange diffchange-inline">images show</del>, in this flare - as with many of the most powerful </div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>As the <ins class="diffchange diffchange-inline">image in Figure 1 shows</ins>, in this flare - as with many of the most powerful </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>events - we are essentially looking deep into the core of the active</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>events - we are essentially looking deep into the core of the active</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>region.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>region.</div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>altitude.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>altitude.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>[[File:149f3.png|thumb|center|<del class="diffchange diffchange-inline">600px</del>|'''Figure 3''': Three panels showing, as </div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>[[File:149f3.png|thumb|center|<ins class="diffchange diffchange-inline">700px</ins>|'''Figure 3''': Three panels showing, as </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>a function of height above the center of a major sunspot, the magnetic field,</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>a function of height above the center of a major sunspot, the magnetic field,</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>the Alfv&eacute;n speed, and the plasma beta.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>the Alfv&eacute;n speed, and the plasma beta.</div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>smaller as well.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>smaller as well.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>That means that the coronal field (intensity and scale) and Alfv&eacute;n speed will </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>That means that the coronal field (intensity and scale) and Alfv&eacute;n speed will </div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>be correspondingly smaller. <del class="diffchange diffchange-inline"> </del></div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>be correspondingly smaller <ins class="diffchange diffchange-inline">in this particular event.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">A survey of a number of representative events will clearly be warranted, and we hope that [http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/Cycle_24_has_begun Cycle 24] will bring us events</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">ten times as powerful</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>== Speculation and Conclusion ==</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>== Speculation and Conclusion ==</div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>the theory of the processes in the corona just above them.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>the theory of the processes in the corona just above them.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>A relativistic Alfv&eacute;n speed means that the [http://en.wikipedia.org/wiki/Flux Poynting flux] can rival </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>A relativistic Alfv&eacute;n speed means that the [http://en.wikipedia.org/wiki/Flux Poynting flux] can rival </div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>the motions of accelerated particles, for example.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>the motions of accelerated particles, for example<ins class="diffchange diffchange-inline">, in terms of the speed of energy transport</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>Although the theory of these phenomena is still at its bare beginnings, it also seems likely that</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>Although the theory of these phenomena is still at its bare beginnings, it also seems likely that</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>such extreme values of Alfv&eacute;n speed and plasma beta will also help to </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>such extreme values of Alfv&eacute;n speed and plasma beta will also help to </div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>gamma rays to speak of?</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>gamma rays to speak of?</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>And yet, there was a</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>And yet, there was a</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>[http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/First_Sunquake_of_Solar_Cycle_24_Observed_by_Solar_Dynamics_Observatory sunquake].</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>[http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/First_Sunquake_of_Solar_Cycle_24_Observed_by_Solar_Dynamics_Observatory sunquake]<ins class="diffchange diffchange-inline">; there have been suggestions that high-energy ions (the sources of flare gamma rays) might be implicated in sunquake</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins class="diffchange diffchange-inline">activity</ins>.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>Does the ion acceleration require a still stronger magnetic field?</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>Does the ion acceleration require a still stronger magnetic field?</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del style="color: red; font-weight: bold; text-decoration: none;">In the Alfv&eacute;nic exhaust of </del></div></td><td colspan="2"> </td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del style="color: red; font-weight: bold; text-decoration: none;">[http://sprg.ssl.berkeley.edu/~stephchow/cartoons/thepages/Duncan.html magnetic reconnection] </del></div></td><td colspan="2"> </td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del style="color: red; font-weight: bold; text-decoration: none;">one might expect the bulk motion to be in the form of relativistic</del></div></td><td colspan="2"> </td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del style="color: red; font-weight: bold; text-decoration: none;">particles, ie that the entire plasma would consist of high-energy particles</del></div></td><td colspan="2"> </td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del style="color: red; font-weight: bold; text-decoration: none;">rather than the usually assumed [Maxwellian distributions].</del></div></td><td colspan="2"> </td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>In any case we now have marvelous tools to study these questions </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>In any case we now have marvelous tools to study these questions </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>observationally, and so we may expect some progress via studies of this</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>observationally, and so we may expect some progress via studies of this</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>and other flares with these tools; this Nugget and the </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>and other flares with these tools; this Nugget and the </div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>[http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/First_Sunquake_of_Solar_Cycle_24_Observed_by_Solar_Dynamics_Observatory sunquakes Nugget] on the same event have </div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>[http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/First_Sunquake_of_Solar_Cycle_24_Observed_by_Solar_Dynamics_Observatory sunquakes Nugget] on the same event have only <ins class="diffchange diffchange-inline">described parts of </ins>the <ins class="diffchange diffchange-inline">rich data available now</ins>.</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>only <del class="diffchange diffchange-inline">begun </del>the <del class="diffchange diffchange-inline">work needed</del>.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div></div></td></tr>
</table>Hhudsonhttps://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=The_Alfven_Speed_above_a_Sunspot,_and_Gamma-rays&diff=4311&oldid=prevHhudson: tidied up, added last figure2011-04-12T11:54:33Z<p>tidied up, added last figure</p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>flares, i.e. that Kahler's "big flare syndrome" (where everything scales</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>flares, i.e. that Kahler's "big flare syndrome" (where everything scales</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>together) does not apply in this case.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>together) does not apply in this case.</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>For this flare, Figure 2 shows that there was negligible [2.2 MeV<del class="diffchange diffchange-inline">] </del></div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>For this flare, Figure 2 shows that there was negligible [<ins class="diffchange diffchange-inline">http://en.wikipedia.org/wiki/Solar_surface_fusion </ins>2.2 MeV gamma-ray emission <ins class="diffchange diffchange-inline">line]</ins>, RHESSI's most sensitive tool for this purpose, and </div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>gamma-ray emission, RHESSI's most sensitive tool for this purpose, and </div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>that the hard X-ray spectrum was weak above 50 keV.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>that the hard X-ray spectrum was weak above 50 keV.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>Many research workers will express surprise at the strength of the</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>Many research workers will express surprise at the strength of the</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>[http://solarscience.msfc.nasa.gov/3dfields.shtml coronal magnetic field]</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>[http://solarscience.msfc.nasa.gov/3dfields.shtml coronal magnetic field]</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div><del class="diffchange diffchange-inline"> </del>above a big spot, </div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>above a big spot, </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>about the [http://en.wikipedia.org/wiki/Alfv&eacute;n_wave Alfv&eacute;n speed],</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>about the [http://en.wikipedia.org/wiki/Alfv&eacute;n_wave Alfv&eacute;n speed],</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>and about the [http://en.wikipedia.org/wiki/Beta_(plasma_physics) plasma beta] </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>and about the [http://en.wikipedia.org/wiki/Beta_(plasma_physics) plasma beta] </div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>below a few Mm above a big spot!</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>below a few Mm above a big spot!</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>Figure 3 details some of these parameters for a conservatively chosen</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>Figure 3 details some of these parameters for a conservatively chosen</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>set of model conditions above a sunspot.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>set of model conditions above a <ins class="diffchange diffchange-inline">very large </ins>sunspot.</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>One of the problems of <del class="diffchange diffchange-inline">this region is that it </del>is so dark and non-emissive</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>One of the problems of <ins class="diffchange diffchange-inline">the corona above a spot umbra </ins>is so dark and non-emissive</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>that ordinary astronomical techniques do not work very well, and so </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>that ordinary astronomical techniques do not work very well, and so </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>in fact there are major observational uncertainties.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>in fact there are major observational uncertainties.</div></td></tr>
<tr><td colspan="2" class="diff-lineno">Line 95:</td>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>]]</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>]]</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>Is this estimation, which is based on </div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>Is this estimation, which is based on [<ins class="diffchange diffchange-inline">http://adsabs.harvard.edu/abs/2000asqu.book.....C </ins>Allen's Astrophysical Quantities],</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>[Allen's Astrophysical Quantities],</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>at all relevant to the particular flare we are discussing?</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>at all relevant to the particular flare we are discussing?</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>Perhaps not directly, since the Hinode magnetographic observations suggest</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>Perhaps not directly, since the Hinode magnetographic observations suggest</div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>manifestations of major flares within sunspots, with new thinking about</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>manifestations of major flares within sunspots, with new thinking about</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>the theory of the processes in the corona just above them.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>the theory of the processes in the corona just above them.</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>A relativistic Alfv&eacute;n speed means that the Poynting flux can rival </div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>A relativistic Alfv&eacute;n speed means that the <ins class="diffchange diffchange-inline">[http://en.wikipedia.org/wiki/Flux </ins>Poynting flux<ins class="diffchange diffchange-inline">] </ins>can rival </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>the motions of accelerated particles, for example.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>the motions of accelerated particles, for example.</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>Although the theory is at its bare beginnings, it also seems likely that</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>Although the theory <ins class="diffchange diffchange-inline">of these phenomena </ins>is <ins class="diffchange diffchange-inline">still </ins>at its bare beginnings, it also seems likely that</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>such extreme values of Alfv&eacute;n speed and plasma beta will also help to </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>such extreme values of Alfv&eacute;n speed and plasma beta will also help to </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>accelerate the particles that RHESSI detects through hard X-rays and gamma</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>accelerate the particles that RHESSI detects through hard X-rays and gamma</div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>But why, in the case of the flare we have illustrated here, were there no</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>But why, in the case of the flare we have illustrated here, were there no</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>gamma rays to speak of?</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>gamma rays to speak of?</div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins style="color: red; font-weight: bold; text-decoration: none;">And yet, there was a</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div><ins style="color: red; font-weight: bold; text-decoration: none;">[http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/First_Sunquake_of_Solar_Cycle_24_Observed_by_Solar_Dynamics_Observatory sunquake].</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>Does the ion acceleration require a still stronger magnetic field?</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>Does the ion acceleration require a still stronger magnetic field?</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>In the Alfv&eacute;nic exhaust of </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>In the Alfv&eacute;nic exhaust of </div></td></tr>
</table>Hhudsonhttps://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=The_Alfven_Speed_above_a_Sunspot,_and_Gamma-rays&diff=4310&oldid=prevHhudson: /* Observations from Hinode and RHESSI */2011-04-12T11:42:53Z<p><span class="autocomment">Observations from Hinode and RHESSI</span></p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>that the hard X-ray spectrum was weak above 50 keV.</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>that the hard X-ray spectrum was weak above 50 keV.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>[[File:149f2.png|thumb|<del class="diffchange diffchange-inline">left</del>|<del class="diffchange diffchange-inline">300px</del>|'''Figure 2''': Time series of counts</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div>[[File:149f2.png|thumb|<ins class="diffchange diffchange-inline">center</ins>|<ins class="diffchange diffchange-inline">400px</ins>|'''Figure 2''': Time series of counts at 50-100 keV (gold) and at 2200-2250 keV (red), the latter a crude indication of the presence or absence of gamma-rays. In this case, despite the X classification of the flare, there were no detectable gamma rays and only a weak 50-100 keV hard X-ray signature.</div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>at 50-100 keV (gold) and at 2200-2250 keV (red), the latter a crude</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div></div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>indication of the presence or absence of gamma-rays.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div></div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>In this case, despite the X classification of the flare, there were no</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div></div></td></tr>
<tr><td class='diff-marker'>-</td><td style="background: #ffa; color:black; font-size: smaller;"><div>detectable gamma rays and only a weak 50-100 keV hard X-ray signature.</div></td><td class='diff-marker'>+</td><td style="background: #cfc; color:black; font-size: smaller;"><div></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>]]</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>]]</div></td></tr>
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</table>Hhudsonhttps://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=The_Alfven_Speed_above_a_Sunspot,_and_Gamma-rays&diff=4307&oldid=prevHhudson at 08:29, 12 April 20112011-04-12T08:29:11Z<p></p>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|second_author = L. Fletcher </div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|second_author = L. Fletcher </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|publish_date = 12 April 2011</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|publish_date = 12 April 2011</div></td></tr>
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<tr><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|previous_nugget = [[Slow Magnetoacoustic Waves in Two-Ribbon Flares]]</div></td><td class='diff-marker'> </td><td style="background: #eee; color:black; font-size: smaller;"><div>|previous_nugget = [[Slow Magnetoacoustic Waves in Two-Ribbon Flares]]</div></td></tr>
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</table>Hhudsonhttps://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=The_Alfven_Speed_above_a_Sunspot,_and_Gamma-rays&diff=4301&oldid=prevHhudson: uploaded text of 1492011-04-12T08:08:27Z<p>uploaded text of 149</p>
<p><b>New page</b></p><div>{{Infobox Nugget<br />
|name = Nugget<br />
|title = The Alfv&eacute;n Speed above a Spot, and Gamma-rays <br />
|number = 148<br />
|first_author = H. Hudson<br />
|second_author = L. Fletcher <br />
|publish_date = 12 April 2011<br />
|next_nugget = TBD<br />
|previous_nugget = [[Slow Magnetoacoustic Waves in Two-Ribbon Flares]]<br />
}}<br />
<br />
== Introduction ==<br />
<br />
It is common for powerful flares to occur actually within sunspots, <br />
with their H-alpha ribbons blithely crossing over these regions of<br />
very strong magnetic field.<br />
What does this association mean for flare theory, and what does it mean<br />
for the interesting differences RHESSI has discovered between flares<br />
with and without gamma-rays?<br />
We discuss these issues in the context of the X-class flare of February 15,<br />
2011.<br />
This was only the second X-class flare of this solar maximum; it was not a<br />
gamma-ray event but it was the source of a clear <br />
[http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/First_Sunquake_of_Solar_Cycle_24_Observed_by_Solar_Dynamics_Observatory sunquake].<br />
<br />
== Observations from Hinode and RHESSI ==<br />
<br />
The flare was well-observed by the [http://sot.lmsal.com/pod SOT] <br />
white-light imager on [http://www.isas.jaxa.jp/home/solar/ Hinode],<br />
with 20-second cadence in three broad-band optical filters. <br />
This data set is quite remarkable because of the excellent resolution<br />
and brilliant image contrast achieved by the SOT telescope, the largest<br />
solar telescope ever put in space.<br />
Figure 1 shows an overlay of the patches of white-light emission extracted<br />
from the several images taken during the <br />
[http://hesperia.gsfc.nasa.gov/hessi/flares.htm impulsive phase] of the flare,<br />
which is when we ordinarily observe hard X-rays and gamma-rays.<br />
<br />
[[File:149f1.png|thumb|center|400px|'''Figure 1''': The bright patches <br />
of the white-light flare emission, shown in different colors for the several<br />
different images at enhanced contrast. The background image is an unaltered<br />
view of the active region, which has well-developed spots. <br />
The white-light flare patches extend well into the umbrae of the spots.<br />
]]<br />
<br />
At the same time as these white-light emissions, what was RHESSI seeing?<br />
Figure 2 offers a simplified view of the RHESSI counting rates, mainly to <br />
illustrate the distinct lack of a gamma-ray signature.<br />
RHESSI has shown that gamma-ray flares are quite different from ordinary<br />
flares, i.e. that Kahler's "big flare syndrome" (where everything scales<br />
together) does not apply in this case.<br />
For this flare, Figure 2 shows that there was negligible [2.2 MeV] <br />
gamma-ray emission, RHESSI's most sensitive tool for this purpose, and <br />
that the hard X-ray spectrum was weak above 50 keV.<br />
<br />
[[File:149f2.png|thumb|left|300px|'''Figure 2''': Time series of counts<br />
at 50-100 keV (gold) and at 2200-2250 keV (red), the latter a crude<br />
indication of the presence or absence of gamma-rays.<br />
In this case, despite the X classification of the flare, there were no<br />
detectable gamma rays and only a weak 50-100 keV hard X-ray signature.<br />
]]<br />
<br />
== Theory ==<br />
<br />
As the images show, in this flare - as with many of the most powerful <br />
events - we are essentially looking deep into the core of the active<br />
region.<br />
In these cases the many signatures of non-thermal effects in the<br />
lower solar atmosphere (hard X-rays, H-alpha, EUV, and intense white<br />
light) all implicate the strong magnetic fields to be found in the<br />
umbra and penumbra regions of major <br />
[http://en.wikipedia.org/wiki/Sunspot sunspots].<br />
<br />
In this Nugget we remind readers that the coronal volume just above<br />
a sunspot is a particularly interesting and ill-understood place.<br />
Many research workers will express surprise at the strength of the<br />
[http://solarscience.msfc.nasa.gov/3dfields.shtml coronal magnetic field]<br />
above a big spot, <br />
about the [http://en.wikipedia.org/wiki/Alfv&eacute;n_wave Alfv&eacute;n speed],<br />
and about the [http://en.wikipedia.org/wiki/Beta_(plasma_physics) plasma beta] <br />
as well - all are extreme, according to the best observational estimates.<br />
The Alfv&eacute;n speed, if computed naively, exceeds the speed of light<br />
below a few Mm above a big spot!<br />
Figure 3 details some of these parameters for a conservatively chosen<br />
set of model conditions above a sunspot.<br />
One of the problems of this region is that it is so dark and non-emissive<br />
that ordinary astronomical techniques do not work very well, and so <br />
in fact there are major observational uncertainties.<br />
The theory behind the extrapolations in Figure 3 is very simple and safe,<br />
though.<br />
For a spot like this we could expect an Alfv&eacute;n speed of c/3 at 10,000 km<br />
altitude.<br />
<br />
[[File:149f3.png|thumb|center|600px|'''Figure 3''': Three panels showing, as <br />
a function of height above the center of a major sunspot, the magnetic field,<br />
the Alfv&eacute;n speed, and the plasma beta.<br />
The assumed parameters for the sunspot are a central field of 3500 G and<br />
an umbral radius of 10,000 km.<br />
]]<br />
<br />
Is this estimation, which is based on <br />
[Allen's Astrophysical Quantities],<br />
at all relevant to the particular flare we are discussing?<br />
Perhaps not directly, since the Hinode magnetographic observations suggest<br />
field intensities about a factor of three smaller, and the spatial scales<br />
smaller as well.<br />
That means that the coronal field (intensity and scale) and Alfv&eacute;n speed will <br />
be correspondingly smaller. <br />
<br />
== Speculation and Conclusion ==<br />
<br />
This Nugget suggests that we begin to combine observations of the <br />
manifestations of major flares within sunspots, with new thinking about<br />
the theory of the processes in the corona just above them.<br />
A relativistic Alfv&eacute;n speed means that the Poynting flux can rival <br />
the motions of accelerated particles, for example.<br />
Although the theory is at its bare beginnings, it also seems likely that<br />
such extreme values of Alfv&eacute;n speed and plasma beta will also help to <br />
accelerate the particles that RHESSI detects through hard X-rays and gamma<br />
rays. <br />
But why, in the case of the flare we have illustrated here, were there no<br />
gamma rays to speak of?<br />
Does the ion acceleration require a still stronger magnetic field?<br />
In the Alfv&eacute;nic exhaust of <br />
[http://sprg.ssl.berkeley.edu/~stephchow/cartoons/thepages/Duncan.html magnetic reconnection] <br />
one might expect the bulk motion to be in the form of relativistic<br />
particles, ie that the entire plasma would consist of high-energy particles<br />
rather than the usually assumed [Maxwellian distributions].<br />
In any case we now have marvelous tools to study these questions <br />
observationally, and so we may expect some progress via studies of this<br />
and other flares with these tools; this Nugget and the <br />
[http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php/First_Sunquake_of_Solar_Cycle_24_Observed_by_Solar_Dynamics_Observatory sunquakes Nugget] on the same event have <br />
only begun the work needed.</div>Hhudson