Magnetic fields and low-frequency acoustic wave-energy supply to the solar chromosphere. (arXiv:1812.05322v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Rajaguru_S/0/1/0/all/0/1">S.P. Rajaguru</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Sangeetha_C/0/1/0/all/0/1">C.R. Sangeetha</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Tripathi_D/0/1/0/all/0/1">Durgesh Tripathi</a> (2) ((1) Indian Institute of Astrophysics, Bangalore, India (2) Inter-University Centre for Astronomy and Astrophysics, Ganeshkhind, India)
The problem of solar chromospheric heating remains a challenging one with
wider implications for stellar physics. Several studies in the recent past have
shown that small-scale inclined magnetic field elements channel copious amount
of energetic low-frequency acoustic waves, that are normally trapped below the
photosphere. These magneto-acoustic waves are expected to shock at
chromospheric heights contributing to chromospheric heating. In this work,
exploiting simultaneous photospheric vector magnetic field, Doppler, continuum
and line-core intensity (of FeI 6173 {AA}) observations from the Helioseismic
and Magnetic Imager (HMI) and lower-atmospheric UV emission maps in the 1700
{AA} and 1600 {AA} channels of the Atmospheric Imaging Assembly (AIA), both
onboard the Solar Dynamics Observatory (SDO) of NASA, we revisit the
relationships between magnetic field properties (inclination and strength) and
the acoustic wave propagation (phase travel time). We find that the flux of
acoustic energy, in the 2 – 5 mHz frequency range, between the upper
photosphere and lower chromosphere is in the range of 2.25 – 2.6 kW m$^{-2}$,
which is about twice the previous estimates. We identify that the relatively
less-inclined magnetic field elements in the quiet-Sun channel a significant
amount of waves of frequency lower than the theoretical minimum for acoustic
cut-off frequency due to magnetic inclination. We also derive indications that
these waves steepen and start to dissipate within the heights ranges probed,
while those let out due to inclined magnetic fields pass through. We explore
connections with existing theoretical and numerical results that could explain
the origin of these waves.
The problem of solar chromospheric heating remains a challenging one with
wider implications for stellar physics. Several studies in the recent past have
shown that small-scale inclined magnetic field elements channel copious amount
of energetic low-frequency acoustic waves, that are normally trapped below the
photosphere. These magneto-acoustic waves are expected to shock at
chromospheric heights contributing to chromospheric heating. In this work,
exploiting simultaneous photospheric vector magnetic field, Doppler, continuum
and line-core intensity (of FeI 6173 {AA}) observations from the Helioseismic
and Magnetic Imager (HMI) and lower-atmospheric UV emission maps in the 1700
{AA} and 1600 {AA} channels of the Atmospheric Imaging Assembly (AIA), both
onboard the Solar Dynamics Observatory (SDO) of NASA, we revisit the
relationships between magnetic field properties (inclination and strength) and
the acoustic wave propagation (phase travel time). We find that the flux of
acoustic energy, in the 2 – 5 mHz frequency range, between the upper
photosphere and lower chromosphere is in the range of 2.25 – 2.6 kW m$^{-2}$,
which is about twice the previous estimates. We identify that the relatively
less-inclined magnetic field elements in the quiet-Sun channel a significant
amount of waves of frequency lower than the theoretical minimum for acoustic
cut-off frequency due to magnetic inclination. We also derive indications that
these waves steepen and start to dissipate within the heights ranges probed,
while those let out due to inclined magnetic fields pass through. We explore
connections with existing theoretical and numerical results that could explain
the origin of these waves.
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