1 Introduction

Type II solar radio bursts seen in dynamic radio spectrograms (Wild & McCready 1950; Wild 1950; Wild et al. 1954; Roberts 1959; Wild 1985) were the first indirect observations of large-scale shock waves in the solar corona. It was Uchida (1960) who correctly associated this phenomenon with collisionless fast-mode magnetohydrodynamic shock waves. The passage of a shock wave in the corona is believed to give rise to plasma oscillations which generate (electrostatic) Langmuir waves which are converted into (electromagnetic) type II burst radio emission. For a recent account of observations and theory related to type II solar radio bursts the reader is referred to Aurass (1997) and Mann (1995), respectively.

Another suggested manifestation of large-scale shock waves on the Sun is the "Moreton wave'' (also known as flare wave). Moreton waves are arc-like features observed in H$\alpha \/$ (6563 Å) (and particularly in off-band H$\alpha \/$) traveling away from an H$\alpha \/$ flare site (Moreton 1960, 1961; Moreton & Ramsey 1960; Ramsey & Smith 1966). The generally accepted physical description of these propagating disturbances in the chromosphere is in terms of a model invoking coronal shock waves (Meyer 1968; Uchida 1968; Uchida et al. 1973).

Recently, there has been considerable interest in 195 Å images from the Extreme Ultraviolet Imaging Telescope (EIT) (Delaboudinière et al. 1995) on board the Solar and Heliospheric Observatory (SOHO) (Domingo et al. 1995) which have shown wave-like structures in the solar corona (Moses et al. 1997; Thompson et al. 1998, 1999). It has been suggested that these bright propagating EUV features are signatures of the coronal shock waves believed to cause chromospheric Moreton waves. Transient propagating disturbances in the corona have also been observed in 195 and 171 Å images from the Transition Region and Coronal Explorer (TRACE) mission (Wills-Davey & Thompson 1999).

Delannée & Aulanier (1999) and Delannée (2000) have suggested that "EIT waves'' are not related to shock waves but merely indicate regions of magnetic field compression or electric currents during a magnetic reconnection process involving the opening of magnetic field lines. However Delannée (2000) did not discuss observations at wavelengths (such as radio or H$\alpha$), which might indicate associations, or otherwise, with shock waves. Two of the three events examined by Delannée (2000) (one of which is the event examined by Delannée & Aulanier 1999) have published reported associations with coronal type II bursts, and hence shock waves (Klassen et al. 2000; Leblanc et al. 2000; Solar Geophysical Data, 641(I), 98; 643(I), 123). The third event on 1998 June 13 is also associated with a type II burst as seen in the Astrophysikalisches Institut Potsdam (AIP) Radio Spectrograph (Mann et al. 1992), although this radio event has not been reported previously, nor the spectrogram published. Based on a qualitative examination of a series of events seen from 1997 November 1-6 Delannée et al. (2000a, 2000b) suggested that EIT waves may simply be bright coronal arcs due to the projection (of the low coronal material) of an expanding bubble-like or loop-like coronal mass ejection onto the solar disk. The event discussed in this paper is one of the events examined by Delannée et al. (2000a, 2000b). As will be seen below we find that the EIT wave associated with this event is closely associated with an H$\alpha$ Moreton wave and a type II burst, suggesting it is related to a shock wave.

Few comparative studies have been carried out examining the relation between EIT waves and radio observations. A comparison of EIT waves with coronal type II bursts seen in spectrograph observations indicates that both may be signatures of the same phenomenon (Klassen et al. 2000). We know of only one published account comparing a type II burst location with an EIT wave (Gopalswamy et al. 2000). Nonetheless, the few results obtained so far do suggest that EIT waves are associated with coronal shock waves. We are aware of three publications comparing EIT waves with Moreton waves (Thompson et al. 2000; Pohjolainen et al. 2001; Warmuth et al. 2001). These found the different wave signatures to be roughly co-spatial, supporting the suggestion that EIT waves may be a coronal counterpart of chromospheric Moreton waves.

Timing arguments and similar values for the derived speeds have been used to support the suggestion of a close relation between Moreton waves and coronal type II bursts (Moreton 1964; Smith 1968; Smith & Harvey 1971; Wild & Smerd 1972). While Kai (1969) found type II burst locations apparently lying on an arc centered on a flare and inferred a relation with a shock wave, the only published account of a direct comparison of type II burst locations with H$\alpha$ Moreton waves is that of Harvey et al. (1974).

To date, there have been only speculative suggestions that some soft X-ray features observed in the solar corona may have been observations of large-scale shock waves. These were based on the behaviour of the soft X-ray features and the apparent overlap in time with metric type II bursts seen in radio spectrograms (Hudson & Karlický 2000; Khan & Hudson 2000).

In this paper we report observations of a transient, large-scale, propagating feature seen in soft X-ray images associated with a major solar flare on 1997 November 3. This event is associated with an H$\alpha \/$ Moreton wave, an EIT wave, and a coronal type II burst. We examine the nature of the soft X-ray disturbance and compare with radio spectrograph data as well as H$\alpha$, EIT 195 Å and radio images. Our results suggest that the soft X-ray disturbance observed in the early stages is the first clearly demonstrated signature of a large-scale coronal shock wave observed in soft X-rays.