ALMA Observations of Solar Spicules in a Polar Coronal Hole
We report observations of solar spicules at millimeter wavelengths (mm- λ ) using the Atacama Large Millimeter/submillimeter Array (ALMA). These are supplemented by observations in optical, ultraviolet (UV), and extreme ultraviolet (EUV) wavelengths. The observations were made on 2018 December 25 of...
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2025-01-01
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| Online Access: | https://doi.org/10.3847/1538-4357/ada445 |
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| author | T. S. Bastian C. Alissandrakis A. Nindos M. Shimojo S. M. White |
| author_facet | T. S. Bastian C. Alissandrakis A. Nindos M. Shimojo S. M. White |
| author_sort | T. S. Bastian |
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| description | We report observations of solar spicules at millimeter wavelengths (mm- λ ) using the Atacama Large Millimeter/submillimeter Array (ALMA). These are supplemented by observations in optical, ultraviolet (UV), and extreme ultraviolet (EUV) wavelengths. The observations were made on 2018 December 25 of the northern polar coronal hole. ALMA obtained time-resolved imaging observations at wavelengths of 3 mm (100 GHz; 2 s cadence) and 1.25 mm (239 GHz; ≈2 minutes cadence) with an angular resolution of 2 $\mathop{.}\limits^{\unicode{x02033}}$ 2 × 1 $\mathop{.}\limits^{\unicode{x02033}}$ 3 and 1 $\mathop{.}\limits^{\unicode{x02033}}$ 5 × 0 $\mathop{.}\limits^{\unicode{x02033}}$ 7, respectively. Spicules observed at mm- λ are easily seen low in the chromosphere whereas spicules in UV bands are seen to extend higher. The spicules observed at mm- λ are seen in absorption against coronal EUV emission, allowing us to estimate the column depth of neutral hydrogen. Spicular emission at mm- λ , due to thermal free–free radiation, allows us to estimate the electron number density as a function of height. We find that spicule densities, inferred from the mm- λ data are uniquely insensitive to assumptions regarding the temperature of plasma in spicules. We suggest that the upward mass flux carried by spicules is unlikely to play a significant role in the mass budget of the solar corona and solar wind, and the transport of hot material into the corona by spicules may not play a significant role in coronal heating. However, the possibility that electric currents, fast kink and torsional waves, or other wave modes carried by spicules may play a role in transporting energy into the solar corona cannot be excluded. |
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| language | English |
| publishDate | 2025-01-01 |
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| series | The Astrophysical Journal |
| spelling | doaj-art-b042d1e0982a4299b202348450fdc4182025-02-04T10:20:08ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-0198016010.3847/1538-4357/ada445ALMA Observations of Solar Spicules in a Polar Coronal HoleT. S. Bastian0https://orcid.org/0000-0002-0713-0604C. Alissandrakis1https://orcid.org/0000-0003-1358-5522A. Nindos2https://orcid.org/0000-0003-0475-2886M. Shimojo3https://orcid.org/0000-0002-2350-3749S. M. White4https://orcid.org/0000-0002-8574-8629National Radio Astronomy Observatory , 520 Edgemont Road, Charlottesville, VA 22903, USA ; tbastian@nrao.eduSection of Astro-Geophysics, Department of Physics, University of Ioannina , GR-45110 Ioannina, GreeceSection of Astro-Geophysics, Department of Physics, University of Ioannina , GR-45110 Ioannina, GreeceNational Astronomical Observatory of Japan , Mitaka, Japan; Graduate University for Advanced Studies , SOKENDAI, Mitaka, JapanSpace Vehicles Directorate , Air Force Research Laboratory, Kirtland AFB, NM, USAWe report observations of solar spicules at millimeter wavelengths (mm- λ ) using the Atacama Large Millimeter/submillimeter Array (ALMA). These are supplemented by observations in optical, ultraviolet (UV), and extreme ultraviolet (EUV) wavelengths. The observations were made on 2018 December 25 of the northern polar coronal hole. ALMA obtained time-resolved imaging observations at wavelengths of 3 mm (100 GHz; 2 s cadence) and 1.25 mm (239 GHz; ≈2 minutes cadence) with an angular resolution of 2 $\mathop{.}\limits^{\unicode{x02033}}$ 2 × 1 $\mathop{.}\limits^{\unicode{x02033}}$ 3 and 1 $\mathop{.}\limits^{\unicode{x02033}}$ 5 × 0 $\mathop{.}\limits^{\unicode{x02033}}$ 7, respectively. Spicules observed at mm- λ are easily seen low in the chromosphere whereas spicules in UV bands are seen to extend higher. The spicules observed at mm- λ are seen in absorption against coronal EUV emission, allowing us to estimate the column depth of neutral hydrogen. Spicular emission at mm- λ , due to thermal free–free radiation, allows us to estimate the electron number density as a function of height. We find that spicule densities, inferred from the mm- λ data are uniquely insensitive to assumptions regarding the temperature of plasma in spicules. We suggest that the upward mass flux carried by spicules is unlikely to play a significant role in the mass budget of the solar corona and solar wind, and the transport of hot material into the corona by spicules may not play a significant role in coronal heating. However, the possibility that electric currents, fast kink and torsional waves, or other wave modes carried by spicules may play a role in transporting energy into the solar corona cannot be excluded.https://doi.org/10.3847/1538-4357/ada445Solar atmosphereSolar spiculesSolar chromosphereSolar ultraviolet emissionSolar radio emissionSolar extreme ultraviolet emission |
| spellingShingle | T. S. Bastian C. Alissandrakis A. Nindos M. Shimojo S. M. White ALMA Observations of Solar Spicules in a Polar Coronal Hole The Astrophysical Journal Solar atmosphere Solar spicules Solar chromosphere Solar ultraviolet emission Solar radio emission Solar extreme ultraviolet emission |
| title | ALMA Observations of Solar Spicules in a Polar Coronal Hole |
| title_full | ALMA Observations of Solar Spicules in a Polar Coronal Hole |
| title_fullStr | ALMA Observations of Solar Spicules in a Polar Coronal Hole |
| title_full_unstemmed | ALMA Observations of Solar Spicules in a Polar Coronal Hole |
| title_short | ALMA Observations of Solar Spicules in a Polar Coronal Hole |
| title_sort | alma observations of solar spicules in a polar coronal hole |
| topic | Solar atmosphere Solar spicules Solar chromosphere Solar ultraviolet emission Solar radio emission Solar extreme ultraviolet emission |
| url | https://doi.org/10.3847/1538-4357/ada445 |
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