Sunspot Plumes Research Articles

Velocities in Sunspot Plumes

We have extended our investigation of sunspot regions, with particular attention to the physics of the transition region between the chromosphere and the corona. In sunspot plumes, the most prominent features in the transition region intensity maps, we find downflows exceeding 25 km s−1. The observations show that the flow cannot be maintained by inflow from the corona and prompt a search for the origin of the flow and its possible relation to the origin of the sunspot plume. We find that the downflows in sunspot plumes are maintained by gas at transition region temperatures, streaming in flow channels from locations well outside the sunspot. Hence, the flow pattern in the transition region shows similarities to the inverse Evershed flow in the chromosphere. We present a working hypothesis that is based on the siphon flow mechanism.

The EUV spectrum of sunspot plumes observed by SUMER on SOHO

We present results from sunspot observations obtained by SUMER on SOHO. In sunspot plumes the EUV spectrum differs from the quiet Sun; continua are observed with different slopes and intensities; emission lines from molecular hydrogen and many unidentified species indicate unique plasma conditions above sunspots. Sunspot plumes are sites of systematic downflow. We also discuss the properties of sunspot oscillations

The EUV Spectrum of Sunspot Plumes Observed by SUMER on SOHO

AbstractWe present results from sunspot observations obtained by SUMER on SOHO. In sunspot plumes the EUV spectrum differs from the quiet Sun; continua are observed with different slopes and intensities; emission lines from molecular hydrogen and many unidentified species indicate unique plasma conditions above sunspots. Sunspot plumes are sites of systematic downflow. We also discuss the properties of sunspot oscillations.

The dynamical and time variable solar transition region observed with the coronal diagnostic spectrometer (CDS) on SOHO

CDS on SOHO has detected an upper solar atmosphere that is more dynamic and time variable than previously expected. Exciting and unexpected is the strongly time variable and dynamic active region loops at transition region temperatures. Loops in the temperature range of 1–5 × 10 5 K, extending 20 000 – 90 000 km above the solar surface, are seen to appear and disappear in less than one hour. Spectral lines from the same loops are frequently Doppler shifted corresponding to plasma velocities of ±50–100 km s −1 in sections of the loops. The dynamic active region loops may be connected to the down-flows seen near sunspots, frequently in sunspot plumes. Other new, time variable and dynamic phenomena are also seen, i.e. the so called “blinkers”, and rotating transition region features. The blinkers occur in the quiet Sun network, with similar phenomena also being seen in active regions. They consist of strong temporal variations in the EUV line emission at transition region temperatures and last a few minutes. The rotating features are macro-spicule like structures, seen both on the limb and on the disk. They show blue- and red-shifted emission on either side of an axis extending above the foot-points. The appearance of variable loops and blinkers show that we need to revise our concepts of the structure of the upper solar atmosphere and the processes going on in these regions, perhaps in the direction of a more fine structured atmosphere.

Structure and dynamics in the atmosphere above sunspot regions

Based on simultaneous observations of 10 EUV emission lines with the Coronal Diagnostic Spectrometer — CDS on the Solar and Heliospheric Observatory — SOHO we study the spatial distributions of both line emission and line-of-sight velocity in the atmosphere above 17 sunspots. We find that both the enhanced EUV line emissions and the velocities are distributed non-uniformly over the sunspot regions. Areas with enhanced line emission tend to be red shifted, but they seldom coincide exactly with areas with enhanced velocity. Bright sunspot plumes with motion directed away from the observer are observed in most of the sunspot regions.

Observations of sunspot transition region oscillations

Oscillations with a period of 3 minutes are observed in the transition region of six sunspots with the Solar and Heliospheric Observatory - SOHO joint observing programme for velocity fields in sunspot regions. Observations of the transition region lines O v λ629 and N v λλ1238, 1242 with the SUMER instrument show significant differences in the amplitude of the 3-minute oscillations from one sunspot to another, both in intensity and line-of-sight velocity. In four sunspots the central part of the umbra is observed. Two of these sunspots show coincidence between the maxima in peak line intensity and velocity directed towards the observer, as is expected for an upward-propagating acoustic wave. The two other sunspots show large oscillation amplitudes and a difference of 25° between maxima in intensity and blue shift. The possible effect of partial wave reflection on the observed phase relation is discussed. For one sunspot only a part of the umbra, close to the penumbra, was observed and the observations show a difference of 50° between maxima in intensity and blueshift. For the smallest sunspot the observations are found to be contaminated by contributions from an area without oscillations. Observed oscillations in line width are small, but probably significant in two sunspots. The observations of NOAA 8378 allow us to compare simultaneous recordings of the oscillations in the chromospheric Si ii λ1260 line with the oscillations in the transition region lines. We question the suggestion by Fludra (1999) that the sunspot transition region oscillations are a typical feature of the sunspot plumes.

ON THE SUNSPOT TRANSITION REGION

The EUV line emission and relative line-of-sight velocity in the transition region between the chromosphere and corona of 36 sunspot regions are investigated, based on observations with the Coronal Diagnostic Spectrometer — CDS and the Solar Ultraviolet Measurements of Emitted Radiation — SUMER on the Solar and Heliospheric Observatory — SOHO. The most prominent features in the transition-region intensity maps are the sunspot plumes. In the temperature range between log T = 5.2 and log T = 5.6 we find that 29 of the 36 sunspots contain one or two sunspot plumes. The relative line-of-sight velocity in sunspot plumes is high and directed into the Sun in the transition region, for 19 of the sunspots the maximum velocity exceeds 25 km s−1. The velocity increases with increasing temperature, reaches a maximum close to log T = 5.5 and then decreases abruptly.

Soho Observations of the Structure and Dynamics of Sunspot Region Atmospheres

We present results from a study of the spatial distributions of line emission and relative line-of-sight velocity in the atmosphere above 17 sunspot regions, from the chromosphere, through the transition region and into the corona, based on simultaneous observations of ten EUV emission lines with the Coronal Diagnostic Spectrometer – CDS on SOHO. We find that the spatial distributions are nonuniform over the sunspot region and introduce the notation 'sunspot loop' to describe an enhanced transition region emission feature that looks like a magnetic loop, extending from inside the sunspot to the surrounding regions. We find little evidence for the siphon flow. Attention is given to the time variations since we observe both a rapid variation with a characteristic time of a few to several minutes and a slow variation with a time constant of several hours to ≈ 1 day. The most prominent features in the transition region intensity maps are the sunspot plumes. We introduce an updated criterion for the presence of plumes and find that 15 out of 17 sunspots contain a plume in the temperature range logT≈5.2–5.6. The relative line-of-sight velocity in sunspot plumes is high and directed into the Sun in the transition region. Almost all the sunspot regions contain one or a few prominent, strongly redshifted velocity channels, several of the channels extend from the sunspot plume to considerable distances from the sunspot. The flow appears to be maintained by plasmas at transition region temperatures, moving from regions located at a greater height outside the sunspots and towards the sunspot. The spatial correlation is high to moderate between emission lines formed in the transition region lines, but low between the transition region lines and the coronal lines. From detailed comparisons of intensity and velocity maps we find transition region emission features without any sign of coronal emission in the vicinity. A possible explanation is that the emission originates in magnetic flux tubes that are too cold to emit coronal emission. The comparisons suggest that gas at transition region temperature occur in loops different from loops with coronal temperature. However, we cannot exclude the presence of transition region temperatures close to the footpoints of flux tubes emitting at coronal temperatures. Regions with enhanced transition region line emission tend to be redshifted, but the correlation between line emission and relative line-of-sight velocity is weak. We extend our conditional probability studies and confirm that there is a tendency for line profiles with large intensities and red shifts (blue shifts) above the average to constitute an increasing (decreasing) fraction of the profiles as the wavelength shift increases.

Erratum

Bright EUV sunspot plumes have been observed in eight out of eleven different sunspot regions with the Coronal Diagnostic Spectrometer -- CDS on SOHO. From wavelength shifts we derive the line-of-sight velocity, relative to the average velocity in the rastered area, 120 arcsec x 120 arcsec. In sunspot plumes we find that the motion is directed away from the observer and increases with increasing line formation temperature, reaches a maximum between 15 and 41 km~s$^{-1}$ close to log T $\approx$ 5.5, then decreases abruptly. The flow field in the corona is not well correlated with the flow in the transition region and we discuss briefly the implication of this finding.

Flows in Sunspot Plumes Detected with the [ITAL]Solar and Heliospheric Observatory[/ITAL

Bright extreme-UV sunspot plumes have been observed in eight out of 11 different sunspot regions with the Coronal Diagnostic Spectrometer on Solar and Heliospheric Observatory. From wavelength shifts, we derive the line-of-sight velocity relative to the average velocity in the rastered area, 120'' × 120''. In sunspot plumes, we find that the motion is directed away from the observer and increases with increasing line formation temperature, reaches a maximum between 15 and 41 km s-1 close to log logT ≈ 5.5, then decreases abruptly. The flow field in the corona is not well correlated with the flow in the transition region, and we discuss briefly the implication of this finding.

Extreme-Ultraviolet Sunspot Plumes Observed with [ITAL]SOHO[/ITAL

Bright EUV sunspot plumes have been observed in five out of nine sunspot regions with the Coronal Diagnostic Spectrometer on the Solar and Heliospheric Observatory. In the other four regions, the brightest line emissions may appear inside the sunspot but are mainly concentrated in small regions outside the sunspot areas. These results are in contrast to those obtained during the Solar Maximum Mission but are compatible with the Skylab mission results. The present observations show that sunspot plumes are formed in the upper part of the transition region, occur in both magnetic unipolar and bipolar regions, and may extend from the umbra into the penumbra.

Strong magnetic fields and inhomogeneity in the solar corona

It is shown that fields of 1800 G can exist in the corona based on observations of gyroresonance emission at 15 GHz at coronal temperatures. The strong fields occur in a small source radiating in the extraordinary (x) mode over the penumbra of a large symmetric sunspot. The optically-thin ordinary mode emission from the region shows a nearby peak at only 36,000 K which may be due to a sunspot plume, and a hole over the umbra consistent with the expected low-density material there. The x-mode source is highly asymmetric, despite the apparent symmetry of the sunspot, and its appearance and location imply that the strongest magnetic fields in the corona are localized in a compact flux tube. 21 refs.

On the electron density in sunspot plumes

Skylab observations of EUV line intensities in sunspot plumes, reported by Noyes et al. (1985), have been used to determine electron densities from theoretical curves of MgVI and MgVIII density-sensitive line ratios.

The Extreme Ultraviolet Spectrum of Sunspot Plumes - Part Two - Spectral Diagnostics and Implications for Cooling

The extreme ultraviolet emission-line spectrum of very intense sunspot plumes is analyzed. Several of the standard density diagnostics suggest a constant density, rather than constant pressure, emitting region. Temperature diagnostic line ratios of several ions yield temperatures below those expected in ionization equilibrium (and observed in the quiet Sun). This provides strong evidence for the suggestion that the internal energy of cooling, falling gas accounts for the observed radiation. The lack of such departures from equilibrium in the quiet Sun demonstrates that downflows are not the dominant source of energy at transition region temperatures. We assess the accuracy of several atomic rate coefficients.

The extreme ultraviolet spectrum of sunspot plumes. I - Observations

view Abstract Citations (80) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The extreme ultraviolet spectrum of sunspot plumes. I - Observations Noyes, R. W. ; Raymond, J. C. ; Doyle, J. G. ; Kingston, A. E. Abstract A complete extreme ultraviolet spectrum of a sunspot plume by the Skylab S-055 spectroheliometer is presented, and the relevant observational details are discussed. Identifications and intensities are given for emission lines and continua in the 303-1343 A range. The emission from lines found between 100,000 and a million K are enhanced by up to a factor of 40 compared with quiet and active region spectra. The emission measure curve for the mean spectrum shows a high double peak at log T = 5.7 and 6.0, reflecting the very inhomogeneous spatial structure of the sunspot plumes. The extremely high signal to noise of the spectrum is used to investigate the electron density and ionization stage of the gas based on line ratio techniques. A model of line emission from a gas cooling by radiation alone at constant density is presented, and the observations are compared with various semiempirical and theoretical models. Publication: The Astrophysical Journal Pub Date: October 1985 DOI: 10.1086/163577 Bibcode: 1985ApJ...297..805N Keywords: Extreme Ultraviolet Radiation; Plumes; Solar Spectra; Sunspots; Ultraviolet Astronomy; Emission Spectra; Inhomogeneity; Ionization; Line Spectra; Plasma Cooling; Space Plasmas; Tables (Data); Solar Physics full text sources ADS |