Off-limb (Spicule) DEM Distribution from SoHO/SUMER Observations

Vanninathan, K., Madjarska, M. S., Scullion, Eamon and Doyle, John Gerard (2012) Off-limb (Spicule) DEM Distribution from SoHO/SUMER Observations. Solar Physics, 280 (2). pp. 425-434. ISSN 0038-0938

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In the present work we derive a Differential Emission Measure (DEM) distribution from a region dominated by spicules. We use spectral data from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on-board the Solar Heliospheric Observatory (SoHO) covering the entire SUMER wavelength range taken off-limb in the Northern polar coronal hole to construct this DEM distribution using the CHIANTI atomic database. This distribution is then used to study the thermal properties of the emission contributing to the 171 Å channel in the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO). From our off-limb DEM we found that the radiance in the AIA 171 Å channel is dominated by emission from the Fe ix 171. 07 Å line and has sparingly little contribution from other lines. The product of the Fe ix 171. 07 Å line contribution function with the off-limb DEM was found to have a maximum at logT max (K)=5. 8 indicating that during spicule observations the emission in this line comes from plasma at transition region temperatures rather than coronal. For comparison, the same product with a quiet Sun and prominence DEM were found to have a maximum at logT max (K)=5. 9 and logT max (K)=5. 7, respectively. We point out that the interpretation of data obtained from the AIA 171 Å filter should be done with foreknowledge of the thermal nature of the observed phenomenon. For example, with an off-limb DEM we find that only 3. 6 % of the plasma is above a million degrees, whereas using a quiet Sun DEM, this contribution rises to 15 %.

Item Type: Article
Uncontrolled Keywords: Corona, Transition region
Subjects: F500 Astronomy
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Paul Burns
Date Deposited: 19 Dec 2018 17:20
Last Modified: 11 Oct 2019 15:01

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