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<p class="MsoNormal" align="center" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;text-align:center;background:white">
<b><span lang="EN-GB" style="font-size:16.0pt;font-family:"Arial","sans-serif";color:#6C6CB7;mso-fareast-language:PT">Radio waves measure atmospheric temperature changes<o:p></o:p></span></b></p>
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<a href="http://images.iop.org/objects/phw/news/17/8/6/PW-2013-08-06-Randall-ionosphere.jpg" title=""A VLF receiving antenna at Palmer Station, Antarctica, operated by Stanford University. (Courtesy: Stanford University)" "><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#AB0000;mso-fareast-language:PT;text-decoration:none"><img border="0" width="500" height="375" id="Imagem_x0020_1" src="cid:image001.jpg@01CEBECB.DA658D50" alt="Descrição: A VLF receiving antenna at Palmer Station, Antarctica"></span></a><span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-fareast-language:PT"><br>
<a href="http://images.iop.org/objects/phw/news/17/8/6/PW-2013-08-06-Randall-ionosphere.jpg" title="A VLF receiving antenna at Palmer Station, Antarctica, operated by Stanford University. (Courtesy: Stanford University)"><span style="color:#AB0000;text-decoration:none">Reflected
radio-wave amplitudes a proxy for varying temperatures?</span></a><o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:13.5pt;background:white">
<span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-fareast-language:PT">Very low frequency (VLF) radio waves can be used to measure temperatures at the mesopause – the lower boundary of the upper atmosphere – according to researchers
in Israel. This new method offers a cheaper and more comprehensive way of analysing the effects of long-term climate change on the upper atmosphere, as well as more short-term phenomena, such as solar storms or thunderstorms.
<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:13.5pt;background:white">
<span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-fareast-language:PT">At the Earth's surface, increasing levels of greenhouse gases – such as carbon dioxide – reflect escaping infrared radiation back towards the ground. This results
in a warming effect. In the upper atmosphere, however, greater concentrations of these gases have the opposite effect. At these low atmospheric densities, carbon dioxide primarily acts instead to radiate heat out to space – and does so more effectively at
these altitudes than oxygen or nitrogen, the other main atmospheric components. <o:p>
</o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:13.5pt;background:white">
<span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-fareast-language:PT">When the upper atmosphere cools, it also gradually shrinks – becoming denser and moving closer to the Earth's surface. This cooling also alters the propagation
paths of radio waves, which pass through the upper atmosphere. <o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:15.0pt;background:white">
<b><span lang="EN-GB" style="font-size:12.0pt;font-family:"Arial","sans-serif";color:#6C6CB7;mso-fareast-language:PT">Clear correlations<o:p></o:p></span></b></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:13.5pt;background:white">
<span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-fareast-language:PT">The researchers' method works, therefore, by measuring the amplitude of VLF radio waves – which originate from navigational beacons – after they have bounced
off the ionosphere, which contains the mesopause. The strength of the received signal is affected by the ionospheric density, which is in turn a product of the temperature. The team was able to observe a clear correlation between upper atmosphere temperatures
– calculated from emissions from carbon dioxide measured by the TIMED satellite's
<a href="http://saber.gats-inc.com/index.php"><span style="color:#AB0000;text-decoration:none">SABER</span></a> instrumentation – and the amplitude of the received radio waves.
<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:13.5pt;background:white">
<span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-fareast-language:PT">"We have found a strong anti-correlation between the intensity/amplitude of low-frequency radio waves measured in our 'backyard' and changes in temperature
of the upper atmosphere/lower ionosphere," paper author <a href="http://www.tau.ac.il/~colin/">
<span style="color:#AB0000;text-decoration:none">Colin Price</span></a>, of Tel Aviv University, told
<i>physicsworld.com</i>. "We found that a cooling/warming of the lower ionosphere (</span><span lang="EN-GB" style="font-size:10.0pt;font-family:"Cambria Math","serif";mso-fareast-language:PT">∼</span><span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-fareast-language:PT">90
km altitude) causes an increase/decrease in the radio wave amplitude." <o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:13.5pt;background:white">
<span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-fareast-language:PT">This
<a href="http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50379/abstract"><span style="color:#AB0000;text-decoration:none">new study</span></a> adds considerably to our knowledge of the temperature changes in the upper atmosphere. While the primary driver of
such fluctuations is the Sun – accounting for 60–70% of the variability – it was not previously possible to systematically measure the exact nature of the remaining shifts.
<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:15.0pt;background:white">
<b><span lang="EN-GB" style="font-size:12.0pt;font-family:"Arial","sans-serif";color:#6C6CB7;mso-fareast-language:PT">Cheap and continuous measurements<o:p></o:p></span></b></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:13.5pt;background:white">
<span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-fareast-language:PT">Previously, direct studies of mesopause temperatures had been difficult and expensive to undertake – with the region being both too low for
<i>in situ</i> measurement by orbital satellites, and yet too high for aeroplanes or weather balloons. The team reports that its ground-based apparatus, however, is easy to use and considerably more cost-effective – with each VLF antenna and processing computer
only costing around a few thousand dollars. The new method also allows for continuous measuring of a specific region of the upper atmosphere – a task that is not possible even with indirect measurements from orbiting satellites, such as
<a href="http://science1.nasa.gov/missions/timed/"><span style="color:#AB0000;text-decoration:none">NASA's TIMED mission</span></a>.
<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:13.5pt;background:white">
<span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-fareast-language:PT">Furthermore, the effect of greenhouse gases on the upper atmosphere is more pronounced than at ground level. Every one degree of warming in the lower atmosphere
is met with a corresponding 10 degrees of cooling in the upper atmosphere. According to Price, this increased effect makes the impact of climate change easier to monitor.
<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:15.0pt;background:white">
<b><span lang="EN-GB" style="font-size:12.0pt;font-family:"Arial","sans-serif";color:#6C6CB7;mso-fareast-language:PT">More in-depth observations<o:p></o:p></span></b></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:13.5pt;background:white">
<span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-fareast-language:PT">"[This] discovery provides great potential of an economical approach for probing this mysterious atmosphere region in the global scale," comments
<a href="http://directory.usu.edu/aggie/71476a/"><span style="color:#AB0000;text-decoration:none">Titus Yuan</span></a>, a physicist at Utah State University, who was not involved in this study. He adds that the new methodology "could enable various critical
scientific topics, such as the impact of global climate change in the upper atmosphere".
<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:13.5pt;background:white">
<span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-fareast-language:PT">To solidify this work, the team is now looking into the possibility of taking more radio-wave observations – and for longer periods of time – from different
locations around the globe. Their current study used radio stations located in Greece, Israel and New Zealand. In addition, the team is looking into comparing its results with other sources of temperature and solar-indices data.
<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:13.5pt;background:white">
<span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-fareast-language:PT">The study is reported in the
<a href="http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50379/abstract"><i><span style="color:#AB0000;text-decoration:none">Journal of Geophysical Research: Atmospheres</span></i></a>.
<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;line-height:15.0pt;background:white">
<b><span lang="EN-GB" style="font-size:11.5pt;font-family:"Arial","sans-serif";color:black;mso-fareast-language:PT">About the author<o:p></o:p></span></b></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white">
<span lang="EN-GB" style="font-size:10.0pt;font-family:"Arial","sans-serif";mso-fareast-language:PT">Ian Randall is a science writer based in New Zealand<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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