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Table 1.

Comparison of the characteristic timescales calculated for the typical values of three coronal plasma non-uniformities in which rapidly decaying slow modes have been observed: warm quiescent loops seen in 171 Å (De Moortel 2009), coronal plumes seen in 193 Å (e.g. Krishna Prasad et al. 2014), and hot dense loops observed in the Fe XIX channel by SUMER (Nakariakov et al. 2019).

Typical value Loop in 171 Å Plume in 193 Å Hot loop in SUMER
(Symbol on plots) (square) (star) (circle)
Temperature, T0 0.63 MK 1.3 MK 6.3 MK
Number density, ne 1.5 × 109 cm−3 0.5 × 109 cm−3 1 × 1010 cm−3
Period, P ≈3−10 min ≈8−18 min ≈10−20 min

𝒯M, B = ∞ 3.2 min 23 min 23 min
𝒯M, B = 34 G 3.2 min 23 min 30 min
(β = 0.01) (β = 0.00) (β = 0.38)
𝒯M, B = 12 G 3.3 min 24 min 81 min
(β = 0.05) (β = 0.03) (β = 3.0)
𝒯M, B = 4 G 4.4 min 29 min 548 min ≃ 9 hr
(β = 0.43) (β = 0.28) (β = 27)

𝒯condB, B = ∞ 10 min 11 min 27 min
𝒯condB, B = 34 G 10 min 11 min 36 min
(β = 0.01) (β = 0.00) (β = 0.38)
𝒯condB, B = 12 G 11 min 12 min 97 min
(β = 0.03) (β = 0.03) (β = 3.0)
𝒯condB, B = 4 G 14 min 14 min 650 min ≃ 11 hr
(β = 0.43) (β = 0.28) (β = 27)

τrad 9.7 min 60 min 70 min

Notes. The three points (T, ρ) are marked on the plots in Fig. 1, and are the same parameters used for the three plots in Fig. 2. The characteristic timescale 𝒯M is calculated using Eq. (20) for heating model ℋ = ρ1/2T−7/2. The thermal conduction damping time 𝒯condB is calculated from Eq. (21) using wavelengths λ = 22 Mm, 100 Mm and 250 Mm respectively. A range of magnetic field strengths (hence β) are presented. The characteristic radiative timescale τrad is calculated from Eq. (29).

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