Direct Measurement Results of the Time Lag of LOS-Velocity Oscillations Between Two Heights in Solar Faculae and Sunspots

Abstract

We present an investigation of line-of-sight (LOS) velocity oscillations in solar faculae and sunspots. To study the phase relations between chromospheric and photospheric oscillations of the LOS velocity, we measured the time lag of the chromospheric signal relative to the photospheric one for several faculae and sunspots in a set of spectral line pairs. The measured time lags are different for different objects. The mean measured delay between the oscillations in the five-minute band in faculae is 50 s for the Si i 10 827Å -He i 10 830Å pair; for the pair Fe i 6569Å -Hα 6563Å the mean delay is 20 s; for the pair Fe i 4551Å -Ba ii 4554Å the mean delay is 7 s; for the pair Si i 8536Å -Ca ii 8542Å the mean delay is 20 s. For the oscillations in the three-minute band in sunspot umbrae the mean delay is 55 s for the Si i 10 827Å -He i 10 830Å pair; for the Fe i 6569Å -Hα 6563Å pair it was not possible to determine the delay; for the Fe i 4551Å -Ba ii 4554Å pair the mean delay is 6 s; for the Si i 8536Å -Ca ii 8542Å pair the mean delay is 21 s. Measured delays correspond to the wave propagation speed which significantly exceeds the generally adopted speed of sound in the photosphere. This raises the question of the origin of these oscillations. The possibility that we deal with slow MHD waves is not ruled out.

Oscillations and Waves in Sunspots

“…With a similar analysis, and using a larger set of photospheric and chromospheric spectral lines, Kobanov et al (2013b) derived similar conclusions as Centeno et al (2006) but with substantially smaller time delays. also traced the variations of the cutoff frequency across the umbra.…”

Negative flare in the He i 10830 Å line in facula

“…The spectral observations were carried out at the Horizontal Solar Telescope in the Sayan Solar Observatory (Kobanov et al 2013(Kobanov et al , 2015. The telescope is located at an altitude of 2000 m above sea level; it provides spatial resolution of 1.0-1.5 arcsec on average.…”

Comparing the main oscillation characteristics in the solar chromosphere and magnetosphere based on studies made in ISTP SB RAS

“…Oscillations in faculae Faculae feature five-minute oscillations in signals of LOS velocities both in the photosphere and in the chromosphere [Kobanov et al, 2013a], although the spatial distribution of the oscillations in faculae is inhomogeneous. In LOS velocity signals, frequencies are higher in regions of intense magnetic field (magnetic hills) and lower closer to the boundaries of faculae [Chelpanov et al, 2015;Chelpanov et al, 2016b].…”