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Astron. Astrophys. 355, 1152-1159 (2000)

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1. Introduction

Macro-spicules appear as columns of chromospheric material extending anywhere from 10 to 60 arcsec above the solar limb. Bohlin et al. (1975) first identified macro-spicules from Skylab spectrograph data in the He II 304 Å line. Their characteristic lifetimes range from 3 to 45 minutes (Dere et al. 1989). Moore et al. (1976, 1977) established that EUV macro-spicules could be associated with H[FORMULA] macro-spicules, which in turn seem to be related to flaring X-ray bright points. Chromospheric mass ejections in coronal holes has also been termed as giant macro-spicules (Loucif 1994). From the H[FORMULA] filtergrams taken from Sacramento Peak Observatory, Loucif (1994) has shown that they may significantly contribute to the fast solar wind. Examination of these structure shows that they are impulsive, recurrent and reach the corona. They seem to be located in the chromospheric network, and follow the assumed open magnetic field lines towards the solar corona. Usually the macro-spicules are prominent in spectral lines formed around [FORMULA] K but are invisible in lines formed above [FORMULA] K. Previous EUV and radio observations suggest that macro-spicules have cool [FORMULA] K plasma cores, with a thin outer sheath not exceeding [FORMULA] K (Withbroe et al. 1976; Habbal & Gonzalez 1991). We report here on the detection of a giant macro-spicule with O V 629 Å ([FORMULA]K), and also with a high temperature coronal line, Mg IX 368 Å ([FORMULA] K).

Previous observations by Hassler et al. (1997) and DeForest et al. (1997) did not find any obvious relationship between macro-spicules observed at the limb and polar plumes higher up, other than they both benefit from the open magnetic field configuration in the coronal hole. DeForest et al. (1997) have suggested (from EIT and MDI image overlays) that polar plumes seem to be related to, and originate from, small EUV bright points corresponding to quiescent, unipolar magnetic flux concentrations on network cell boundaries.

Pike & Harrison (1997) first reported the detection of a macro-spicule from a raster scan of CDS. They detected high velocity flows within the macro-spicule. Pike & Mason (1998) have further studied several macro-spicule-like dynamic events in polar regions and have indicated the presence of rotating plasma within the macro-spicule, which they named solar tornados . In contrast to earlier CDS raster scans, our temporal series allow us to study the dynamics of these events with better precision. Very recently, Parenti et al. (1999) have analysed a raster scan in the south polar coronal hole, including a macro-spicule and have presented information on density, temperatures and abundances.

Although spicules have been observed for many years, very little is known about their role in the transport of mass and energy between the chromosphere and higher layers of the Sun. The present investigation is concerned with an analysis of the temporal behaviour of the polar plume plasma. However during our temporal observations we also detected, quite by chance, a macro-spicule or small scale jet within the plume structure.

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© European Southern Observatory (ESO) 2000

Online publication: March 21, 2000