Kennelly–Heaviside layer

<h2 id="history">History</h2>
Existence of a reflective layer was predicted in 1902 independently and almost simultaneously by the American electrical engineer <a href="/facts/Arthur_Edwin_Kennelly/MjkargSj">Arthur Edwin Kennelly</a> (1861–1939)<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a> and the British polymath <a href="/facts/Oliver_Heaviside/ktYBpAt7">Oliver Heaviside</a> (1850–1925), as an explanation for the propagation of radio waves beyond the horizon observed by <a href="/facts/Guglielmo_Marconi/U7HXnDnq">Guglielmo Marconi</a> in 1901. However, it was not until 1924 that its existence was shown by British scientist <a href="/facts/Edward_V._Appleton/7FfJIqz5">Edward V. Appleton</a>,<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> for which he received the 1947 <a href="/facts/Nobel_Prize_in_Physics/o6w1nCbr">Nobel Prize in Physics</a>.<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a>
Physicists resisted the idea of the reflecting layer for one very good reason; it would require <a href="/facts/Total_internal_reflection/Tm0M62NQ">total internal reflection</a>, which in turn would require that the speed of light in the ionosphere would be greater than in the atmosphere below it. Since the latter speed is essentially the same as the speed of light in vacuum (<a href="/facts/Speed_of_light/sKSQwdNx">c</a>), scientists were unwilling to believe the speed in the ionosphere could be higher. Nevertheless, Marconi had received signals in Newfoundland that were broadcast in England, so clearly there must be some mechanism allowing the transmission to reach that far. The paradox was resolved by the discovery that there were two velocities of light, the <a href="/facts/Phase_velocity/m43q3X33">phase velocity</a> and the <a href="/facts/Group_velocity/HPIMFwaV">group velocity</a>. The phase velocity can in fact be greater than c, but the group velocity, being capable of transmitting information, cannot, by <a href="/facts/Special_relativity/vsFFc63E">special relativity</a>, be greater than c. The phase velocity for radio waves in the ionosphere is indeed greater than c, and that makes total internal reflection possible, and so the ionosphere can reflect radio waves. The geometric mean of the phase velocity and the group velocity cannot exceed c, so when the phase velocity goes above c, the group velocity must go below it. 
In 1925, Americans <a href="/facts/Gregory_Breit/FQWwQEgv">Gregory Breit</a> and <a href="/facts/Merle_A._Tuve/Xr0m8PIB">Merle A. Tuve</a> first mapped the Heaviside layer's variations in altitude. The <a href="/facts/ITU/xnT5QSEl">ITU</a> standard model of absorption and reflection of radio waves by the Heaviside Layer was developed by the British Ionospheric physicist <a href="/facts/Louis_Miles_Muggleton/XVsBH2Fe">Louis Muggleton</a><a class="footnote-ref" id="fnref:8" href="#fn:8">8</a> in the 1970s.

<h2 id="etymology">Etymology</h2>
Around 1910, <a href="/facts/William_Eccles_(physicist)/8KA3rcgM">William Eccles</a> proposed the name "Heaviside Layer" for the radio-wave reflecting layer in the upper atmosphere,<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> and the name has subsequently been widely adopted.<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a> The name Kennelly–Heaviside layer was proposed in 1925 to give credit to the work of Kennelly,<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a><a class="footnote-ref" id="fnref:12" href="#fn:12">12</a> which predated the proposal by Heaviside by several months.

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Van_Allen_Belt/XKnhnWK0">Van Allen Belt</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Griffiths, Hugh (15 November 2018). "Oliver Heaviside and the Heaviside layer", Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 376: No. 2134. https://doi.org/10.1098/rsta.2017.0459. Retrieved 14 June 2019. <a href="https://royalsocietypublishing.org/doi/full/10.1098/rsta.2017.0459" target="_blank">https://royalsocietypublishing.org/doi/full/10.1098/rsta.2017.0459</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Marchant, E. W. (Dec. 1916). "The Heaviside layer", Proceedings of the Institute of Radio Engineers, 4, No. 6, pp. 511–520. <a href="https://ieeexplore.ieee.org/abstract/document/1646012" target="_blank">https://ieeexplore.ieee.org/abstract/document/1646012</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">McAdie, Alexander (22 May 1925) "The Kennelly-Heaviside Layer", Science, 61, No 1586, pp. 540 DOI: 10.1126/science.61.1586.540 <a href="https://www.science.org/doi/10.1126/science.61.1586.540.a" target="_blank">https://www.science.org/doi/10.1126/science.61.1586.540.a</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">Martyn, D. F. (1934). "Atmospheric Pressure and the Ionisation of the Kennelly-Heaviside Layer". Nature. 133 (3356): 294. Bibcode:1934Natur.133R.294M. doi:10.1038/133294b0. ISSN 0028-0836. S2CID 684206. <a href="https://doi.org/10.1038%2F133294b0" target="_blank">https://doi.org/10.1038%2F133294b0</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">Russell, A. (24 October 1925). "The “Kennelly-Heaviside” Layer", Nature 116, p. 609. doi:10.1038/116609c0 <a href="https://www.nature.com/articles/116609c0#citeas" target="_blank">https://www.nature.com/articles/116609c0#citeas</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Appleton, Edward V., and Barnett, M. A. F. (1 December 1925). "On some direct evidence for downward atmospheric reflection of electric rays", Proceedings of the Royal Society of London, Series A, Containing Papers of a Mathematical and Physical Character, 109.752 pp. 621–641. <a href="https://royalsocietypublishing.org/doi/abs/10.1098/rspa.1925.0149" target="_blank">https://royalsocietypublishing.org/doi/abs/10.1098/rspa.1925.0149</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">"Nobel Prizes for 1947: Sir Edward Appleton, G.B.E., K.C.B., F.R.S.", Nature, 160, pp. 703–704 (22 November 1947) doi:10.1038/160703c0 <a href="https://www.nature.com/articles/160703c0" target="_blank">https://www.nature.com/articles/160703c0</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">L.M. Muggleton (1975). "A method of predicting foE at any time and place". ITU Telecommunication Journal. 42: 413–418. Bibcode:1975ITUTJ..42..413M. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Griffiths, Hugh (15 November 2018). "Oliver Heaviside and the Heaviside layer", Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 376: No. 2134. https://doi.org/10.1098/rsta.2017.0459. Retrieved 14 June 2019. <a href="https://royalsocietypublishing.org/doi/full/10.1098/rsta.2017.0459" target="_blank">https://royalsocietypublishing.org/doi/full/10.1098/rsta.2017.0459</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Marchant, E. W. (Dec. 1916). "The Heaviside layer", Proceedings of the Institute of Radio Engineers, 4, No. 6, pp. 511–520. <a href="https://ieeexplore.ieee.org/abstract/document/1646012" target="_blank">https://ieeexplore.ieee.org/abstract/document/1646012</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">McAdie, Alexander (22 May 1925) "The Kennelly-Heaviside Layer", Science, 61, No 1586, pp. 540 DOI: 10.1126/science.61.1586.540 <a href="https://www.science.org/doi/10.1126/science.61.1586.540.a" target="_blank">https://www.science.org/doi/10.1126/science.61.1586.540.a</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Russell, A. (24 October 1925). "The “Kennelly-Heaviside” Layer", Nature 116, p. 609. doi:10.1038/116609c0 <a href="https://www.nature.com/articles/116609c0#citeas" target="_blank">https://www.nature.com/articles/116609c0#citeas</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
</ol>

Kennelly–Heaviside layer open-in-new

Kennelly–Heaviside layer