[3] Turbulent velocities of coronal plasma are determined from the observed half widths of spectral line profiles using the known technique [Delone et al., 2003b]. The Doppler width of an optically thin line profile DlD after correction for the instrumental broadening is related to the temperature T and the turbulent velocity x by the equation
| (1) |
 | (2) |
106.
[4] To find turbulent velocities, we have reanalyzed the profiles of the 5303 Å (Fe XII) line measured during total solar eclipses of 1968, 1981, 1990, and 1999 [Delone and Makarova, 1969, 1975; Delone et al., 1989a, 1989b, 2002a, 2002b, 2003a]. We have managed to determine turbulent velocities in morphologically different regions of the corona: quiet corona (QC), coronal hole (CH), and quiescent prominence cavity (QPC).
[5] During the solar eclipse on 11 August 1999 a horizontal solar instrument consisting of two coelostat mirrors feeding two parallel tubes with identical optical and signal registration systems was used to photograph the solar corona [Delone et al., 2002b]. We used the Fabry-Perot interferometers for the Ha, K Ca II and Fe XIV lines with the corresponding narrow interferometric filters as premonochromators. Detailed description of the instruments is given by Delone et al. [2002b]. At the beginning the task of observations was to investigate the directed bulk plasma motions in the solar corona. Later the interferometric coronal line profiles obtained during the 1968, 1981, and 1999 eclipses were reanalyzed to determine the turbulent velocities. Two quiet prominences were seen at the eastern solar limb and two small coronal holes on the disc of the sun located close by the limb were observed. This provides a chance to compare the nonthermal velocities determined from the 5303 Å line profiles for different coronal structures QPC, CH, and QC.
[6] On the images obtained on 11 August 1999, we have also found the
regions with cool coronal emission (CCE). The mean turbulent
velocities in the coronal cavities around the bulks of cold plasma
with
T 
5 104 K-
1.3 105 K turned out to be
32.5 km s-1 [Delone et al., 2003a].
[7] The obtained data together with the results given for various structural formations by other authors are listed in Table 1: the date, information on the instrument and wavelengths, turbulent velocity ( x ) in various coronal formations, and references. Table 1 the references concerning the observations during 1968, 1981 eclipses are indicated, and the values of turbulent velocities x in the various coronal formations are presented. The x values have been determined resulting from reanalyzing the obtained earlier eclipses data. Delone et al. [2003b] collected data from publications devoted to the investigation of the turbulent velocities in the quiet corona and based both on the ground and space observations. The observation were performed in the far ultraviolet spectral region (330-1500 Å) and in the visual l= 5303 Å, l=6374 Å, l=5694 Å. The compiled results provide large amount of data in a statistic sense. For example, the observations of Chae and Schühle [1998] and Chae et al. [2000] on SUMER SOHO during the period from April 1996 to April 1997 were used. In other papers observations during several days were analyzed. In this compilation we have also included the values of turbulent velocities for the quiet corona obtained by the authors by reanalyzing the line profiles measured on the 1981 interferograms. From all these results it follows that the averaged value is equal to 18 km s-1, the range of the velocities is from 10 to 30 km s-1.
[8] Using the observations on board SUMER SOHO during several months in 1996-1997 in the Mg IX 706 Å and 750 Å lines and Si VIII 1440 Å and 1445 Å lines near the southern and northern poles of the Sun over coronal holes, Wilhelm et al. [1998] did not try to separate the line half widths into the thermal and turbulent components and gave only the full Doppler velocities that correspond to the Doppler half widths of the lines. However, if we adopt the temperature T being equal to the commonly accepted temperature of the formation of the lines lgT( Mg IX)=5.95 and lgT( Si VIII)=5.99 then it becomes possible to calculate the values of the nonthermal velocities in coronal holes using the data of Wilhelm et al. [1998]. So we have found that x varies from 30 to 80 km s-1. The average value is x =45 km s-1, which is larger than in the surrounding corona.
[9] The tabulated data display a noticeable scatter. It may be caused
either by actual differences between the studied regions or by
inaccuracies in the technique, mainly in the determination of the
continuum background. The analysis of the data of Table 1 allows
us to conclude that the turbulent velocities in the three
considered regions of the corona follow the relationships:
x
[10] According to numerous investigations a coronal hole is cooler than the quiet corona. If we assume for CH a lower temperature, as obtained in some papers, then the latter inequality will be even stronger. For the eclipse of 1999 we have obtained from the interferogram of the green coronal line [Delone et al., 2002a, 2003a] the values of x simultaneously in the same system for all three discussed regions of the corona.
[11] As known, loop formations are also typical of the low corona. They are observed in a broad wavelength range and extend to a height of several tens (up to several hundreds) of thousands of kilometers above the solar surface. The loops differ in their temperature (from 104 to 106 K), density, and dynamics. In stationary loops 10 < x< 20 km s-1, and these values are characteristic for both "cool" and "hot" loops [Chae et al., 2000; Hara and Ichimoto, 1999; Harra-Murnion et al., 1999; Ichimoto et al., 1995]. As shown by Chae et al. [2000], in dynamic loops turbulent velocities are appreciably higher ( 38 < x< 60 km s-1). We discussed possible interpretation of the observational results and relationship of x with magnetic field (MF) parameters earlier by Delone et al. [2003a] and Yakunina et al. [2004].
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