Dynamics of the solar chromosphere

Abstract

Abstract. We analyze oscillations in the solar atmosphere using image sequences from the Transition Region and Coronal Explorer (TRACE) in three ultraviolet passbands which sample the upper solar photosphere and low chromosphere. We exploit the absence of atmospheric seeing in TRACE data to furnish comprehensive Fourier diagnostics (amplitude maps, phase-difference spectra, spatio-temporal decomposition) for quiet-Sun network and internetwork areas with excellent sampling statistics. Comparison displays from the ground-based Ca ii H spectrometry that was numerically reproduced by Carlsson & Stein are added to link our results to the acoustic shock dynamics in this simulation. The TRACE image sequences confirm the dichotomy in oscillatory behaviour between network and internetwork and show upward propagation above the cutoff frequency, the onset of acoustic shock formation in the upper photosphere, phase-difference contrast between pseudo-mode ridges and the interridge background, enhanced three-minute modulation aureoles around network patches, a persistent low-intensity background pattern largely made up of internal gravity waves, ubiquitous magnetic flashers, and low-lying magnetic canopies with much low-frequency modulation. The spatio-temporal occurrence pattern of internetwork grains is found to be dominated by acoustic and gravity wave interference. We find no sign of the high-frequency sound waves that have been proposed to heat the quiet chromosphere, but such measurement is hampered by non-simultaneous imaging in different passbands. We also find no signature of particular low-frequency fluxtube waves that have been proposed to heat the network. However, internal gravity waves may play a role in their excitation.

Observations of the Sun at Vacuum-Ultraviolet Wavelengths from Space. Part II: Results and Interpretations

“…Incomplete data caused the stripes on the right-hand side (Fig. 3 of Krijger et al 2001) Kjeldseth-Moe 1994; . The results yield a minimum brightness temperature between 4450 K and 4520 K at the top of the photosphere, in good agreement with the value of 4430 K ± 50 K found by Samain et al (1975) from the continuum around 158 nm, and that of 4400 K near 160 nm by Parkinson and Reeves (1969).…”

“…First discovered as oscillations with a period of 300 s in the photosphere and chromosphere (Leighton et al 1962), they subsequently were also seen in VUV emission lines, both in radiance and velocity (Chapman et al 1972;Chipman 1977;Martic et al 1991;Hoekzema et al 1997;Curdt and Heinzel 1998;Hansteen et al 2000;Krijger et al 2001). studied oscillations in the chromosphere using SOHO and the Transition Region and Coronal Explorer (TRACE) ) continuum observations in the 170 nm band.…”

Dynamical Behavior of the Upper Solar Photosphere

“…It shows (k h , f ) Fourier decomposition for the ∆φ(1700−1600) brightness modulation phase differences, determined from simultaneous 1700Å and 1600Å image sequences in the same TRACE data set as used in Figs. 3-4. It shows phase contrast along the pseudo-ridges which is discussed in more detail in Krijger et al (2001). What is important here is the dark wedge of negative phase under the Lamb line, with high coherence.…”

“…Recently, gravity waves showed up rather clearly in similar (k h , f ) phasedifference spectra derived from 1700Å and 1600Å image sequences from TRACE by Krijger et al (2001). Ultraviolet image sequences are perhaps the best diagnostic for gravity waves because they sample intensity rather than velocity (gravity waves primarily affect the temperature), sample them high up (gravitywave intensity modulation grows steeply with height), permit two-wavelength phase-difference evaluation over relatively small height of formation difference (so that a slanted wave remains on-pixel between the two) and TRACE has just sufficient angular resolution (1 arcsec).…”

“…In addition, TRACE offers co-spatial white light imaging at the same resolution. Figure 3 sets the stage in the form of a (k h , f ) power spectrum derived from a TRACE 1700Å image sequence of 3.7 hours duration (details in Krijger et al 2001). It holds for the full field of observation including network, but the latter was so quiet that this figure may be taken as representative of internetwork only.…”