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Astron. Astrophys. 361, 759-765 (2000)

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1. Introduction

H[FORMULA] surges have been studied for more than 50 years (see Roy 1973a, b). They are straight or slightly curved ejections that reach peak velocities of 50-200 km s-1. They reach heights of up to 200,000 km and typically last 10-20 minutes. The surge material either fades or returns into the chromosphere along the trajectory of ascent (Svestka 1976; Tandberg-Hanssen 1977; Foukal 1990). At high spatial resolution, it is evident that the H[FORMULA] surges are highly filamentary in structure (Roy 1973a; Zirin 1988, pp. 296-301). On the other hand, X-ray jets were revealed by the Soft X-ray Telescope (SXT) of YOHKOH (Tsuneta et al. 1991). Their characteristics have been carefully described (Shibata et al. 1992a; Shibata et al. 1994; Schmieder et al. 1995). Of particular interest have been efforts to identify the relationship between cool plasma ejection, represented by H[FORMULA] or H[FORMULA] surges, and hot plasma ejection, represented by brightening or jets seen in EUV and X-ray. Rust et al. (1977) found that few H[FORMULA] surges were coincident with noticeable changes in X-ray emission. Schmieder et al. (1988) compared H[FORMULA] surge observations with relevant UV and X-ray data and supported the idea that H[FORMULA] surges are spatially correlated with UV and X-ray emissions. Shibata et al. (1992a) presented an example which showed that an X-ray jet is nearly co-spatial with an H[FORMULA] surge. However, Canfield et al. (1996) reported that X-ray jets are not co-spatial with H[FORMULA] surges, even though they are associated with each other. Recently, a similar result was obtained by Chae et al. (1999), who showed that the H[FORMULA] surges are not co-spatial with the EUV jets. In brief, most of the previous studies seem to support that H[FORMULA] surges are associated with EUV/X-ray brightening and jets, but the temporal and spatial relationship between them is still not clear.

There are many models devoted to the interpretation of solar dynamic phenomena such as surges and jets (see the detailed discussion by Schmieder et al. 1995, and Canfield et al. 1996). It is well accepted that surges are closely correlated with newly emerging flux in the periphery of sunspots or large-flux concentrations. They are manifestations of the magnetic reconnection between newly emerging and pre-existing flux. In a few careful studies (Schmieder et al. 1995; Yokoyama & Shibata, 1995; and Canfield et al. 1996), H[FORMULA] surges and X-ray jets are viewed as cool and hot components of plasma ejecta, respectively, and both hot and cool plasma are accelerated in a single magnetic reconnection. Since a surge is an outward ejection in the chromosphere, the reconnection site at the surge base could not be very high in the atmosphere, say, somewhere in the photosphere or lower chromosphere. Although the reconnection in the lower atmosphere is able to account for the cool plasma ejection, it seems to be difficult to interpret the creation of X-ray jets (the hot plasma ejection).

In this paper, we described in detail the interacting threads in an H[FORMULA] surge and the subsequent X-ray jet, as well as the associated magnetic environment and evolution. This example shows that the H[FORMULA] surge appears much earlier, caused by the magnetic reconnection in the lower atmosphere, while the X-ray jet appears well after, possibly caused by a fast reconnection in the upper atmosphere.

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© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001
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