Oscillations and running waves observed in sunspots
Осцилляции и бегущие волны, наблюдаемые в солнечных пятнах
2001-08-01
SCID: 54.1/y2nad4t2
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Doppler shiftHα spectroscopyphotospheric wavesrunning penumbral wavessunspot oscillations
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Abstract (AI)
We continue our study of waves and oscillations observed in sunspots using an improved method for enhancing the waves, giving the opportunity to identify them and determine their properties in far Hα wings. We found that the running penumbral waves are observable at least up to the formation height of the H Å line, but not in the H Å or the Å. We found a time lag between the waves in the blue and the red wing of the Hα line corresponding to a phase shift of 180°, that indicates a pure Doppler shift of the line. There is a lag in the propagation of the waves seen at Hα center and at Hα wings. Also there is a lag in the variation of the umbral oscillations as they are observed from lower to higher atmospheric layers. The correlation between umbral oscillations at various atmospheric heights and running penumbral waves strongly indicates that the latter are excited by photospheric umbral oscillations and not the chromospheric ones. We found a new category of photospheric waves that originate at approximately 0.7 of the distance between the umbra and the penumbra boundary and propagate beyond the outer penumbra boundary with a velocity of the order of 3-4 km s-1. Further, we found 3 min penumbral oscillations apparent in the inner penumbra at lower chromospheric layers (far Hα wings).
Key Findings
1
A 180° phase shift between blue- and red-wing signals indicates that the observed Hα-wave variation is a pure Doppler shift.
2
An improved wave-enhancement method identifies sunspot oscillations and waves in far Hα wings and enables determination of their properties.
3
Correlations indicate that running penumbral waves are excited by photospheric rather than chromospheric umbral oscillations; a new photospheric-wave category propagates outward at approximately 3–4 km s−1.
4
Propagation and temporal lags occur between Hα-center and wing waves, and between umbral oscillations observed at progressively higher atmospheric layers.
5
Running penumbral waves are observable up to the Hα-wing formation height, but not in the Hα center or higher sampled wavelengths.
Research Object
Sunspot atmospheric waves and oscillations, including running penumbral waves, umbral oscillations, and newly identified photospheric waves
Research Subject
Wave propagation, phase and time lags across Hα line formation heights and atmospheric layers, Doppler shifts, and the excitation relationship between umbral oscillations and running penumbral waves
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2001-08-01
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