<p>The twisting, ever-shifting and elusive magnetic fields of the Sun’s ephemeral outer atmosphere can now be mapped, thanks to a new method devised by an international team of physicists including Indian researchers.</p>.<p>The technique, presented in a new study published in the journal <em>Science </em>on Thursday, could be used to greatly enhance the understanding of conditions in corona – the mysterious poorly studied outer region of the Sun.</p>.<p>The solar corona – the tenuous outermost layer of the Sun’s atmosphere – consists of a hot and highly diffuse plasma halo extending thousands of kilometres above the star’s burning surface. For years it intrigued scientists with several unresolved questions.</p>.<p>One of the crucial among them is a puzzle related to its temperature. The temperature at the core of the Sun is close to 15 million degrees Celsius, which drops to mere 5,700 degrees at the solar surface (photosphere). But above the photosphere, the temperature starts to increase again with height, reaching one million degrees or more in the corona. What causes such a temperature rise in corona despite moving away from the core is a mystery.</p>.<p>Also, the Sun is a magnetised star and its magnetic field plays a critical role in shaping the solar atmosphere. The 11-year solar cycle, the spectacular solar eruptions and the million-degree solar corona are all driven or governed by the evolution of the solar magnetic field.</p>.<p>But the measurement of the magnetic field is possible only at the solar surface level. The first such measurement was carried out more than a century ago, but there’s still no way to measure the magnetic field of the upper atmosphere.</p>.<p>"We still do not have a precise knowledge of the magnetic field in the upper solar atmosphere, especially the corona, which impedes our complete understanding of the solar magnetism and its interaction with the solar plasma,” team member Tanmoy Samanta, a researcher at George Mason University, USA and a former PhD scholar at Indian Institute of Astrophysics, Bengaluru told <em>DH</em>.</p>.<p>Samanta is a member of an international team led by solar physicists from Peking University, China and National Center for Atmospheric Research, USA, which has measured the global magnetic field of the solar corona for the first time using observations from the Coronal Multi-channel Polarimeter (a coronagraph with 20 cm aperture), an instrument operated by NCAR’s High Altitude Observatory. A physicist from Banaras Hindu University is also a member of the team.</p>.<p>The researchers used their novel technique to derive maps of the magnetic field across the entire observable corona and claimed that such a method could be used to produce routine magnetic field maps similar to those available for the Sun’s surface.</p>.<p>“This is the first time that a global map of the coronal magnetic field has been obtained through actual coronal observations, thus marking a leap towards solving the problem of coronal magnetic field measurements,” Samanta said.</p>
<p>The twisting, ever-shifting and elusive magnetic fields of the Sun’s ephemeral outer atmosphere can now be mapped, thanks to a new method devised by an international team of physicists including Indian researchers.</p>.<p>The technique, presented in a new study published in the journal <em>Science </em>on Thursday, could be used to greatly enhance the understanding of conditions in corona – the mysterious poorly studied outer region of the Sun.</p>.<p>The solar corona – the tenuous outermost layer of the Sun’s atmosphere – consists of a hot and highly diffuse plasma halo extending thousands of kilometres above the star’s burning surface. For years it intrigued scientists with several unresolved questions.</p>.<p>One of the crucial among them is a puzzle related to its temperature. The temperature at the core of the Sun is close to 15 million degrees Celsius, which drops to mere 5,700 degrees at the solar surface (photosphere). But above the photosphere, the temperature starts to increase again with height, reaching one million degrees or more in the corona. What causes such a temperature rise in corona despite moving away from the core is a mystery.</p>.<p>Also, the Sun is a magnetised star and its magnetic field plays a critical role in shaping the solar atmosphere. The 11-year solar cycle, the spectacular solar eruptions and the million-degree solar corona are all driven or governed by the evolution of the solar magnetic field.</p>.<p>But the measurement of the magnetic field is possible only at the solar surface level. The first such measurement was carried out more than a century ago, but there’s still no way to measure the magnetic field of the upper atmosphere.</p>.<p>"We still do not have a precise knowledge of the magnetic field in the upper solar atmosphere, especially the corona, which impedes our complete understanding of the solar magnetism and its interaction with the solar plasma,” team member Tanmoy Samanta, a researcher at George Mason University, USA and a former PhD scholar at Indian Institute of Astrophysics, Bengaluru told <em>DH</em>.</p>.<p>Samanta is a member of an international team led by solar physicists from Peking University, China and National Center for Atmospheric Research, USA, which has measured the global magnetic field of the solar corona for the first time using observations from the Coronal Multi-channel Polarimeter (a coronagraph with 20 cm aperture), an instrument operated by NCAR’s High Altitude Observatory. A physicist from Banaras Hindu University is also a member of the team.</p>.<p>The researchers used their novel technique to derive maps of the magnetic field across the entire observable corona and claimed that such a method could be used to produce routine magnetic field maps similar to those available for the Sun’s surface.</p>.<p>“This is the first time that a global map of the coronal magnetic field has been obtained through actual coronal observations, thus marking a leap towards solving the problem of coronal magnetic field measurements,” Samanta said.</p>
