Intensity and velocity oscillations have been observed in the chromosphere above sunspots for over thirty years (Beckers & Tallant 1969; Beckers & Schultz 1972; Gurman et al. 1982; Lites et al. 1982). These oscillations have since been observed in the transition region, using space-based instruments observing in the extreme ultra-violet (EUV) (see, Fludra 2001; O'Shea et al. 2002; Rendtel et al. 2003; Brynildsen et al. 2004, and references within). Additionally, space-based EUV bandpass imagers have observed periodic intensity propagations along diffuse, fan-like, coronal loop structures (Berghmans & Clette 99; Nightingale et al 1999, De Moortel 2002a). De Moortel (2002b) observe a relationship between 3-minute propagations found within sunspot coronal loops, and 5-minute propagations found within plage coronal loops. In Marsh et al.(2003) we present an observation of a 5-minute propagating wave within a plage coronal loop; the intensity oscillation of the wave was also observed simultaneously at transition region temperatures, suggesting wave propagation through the transition region into the corona along the active region loops. Depontieu et al. (2005) also discuss the possibility of channeling the 5-min photospheric oscillations into the corona along the magnetic field.
The bright solar network, defined by the boundaries of supergranular flows, is dominated by magnetohydrodynamic (MHD) processes and contains oscillations with periods above of the acoustic cut-off (Goodman 2000). Regions of enhanced emission have the strongest magnetic fields and constitute the most intense radiative losses. The microstructure of these fields and their interactions with the convection zone supply energy to the overlying layers. The granular buffeting of flux tubes in the photosphere can create transverse waves which may mode couple to longitudinal waves and can be observed through variations in the plasma emission and radial velocity.
In Marsh & Walsh (2006) we present new, spatially resolved, monochromatic imaging data of a sunspot region at transition region temperatures, combined with simultaneous bandpass imaging of the emerging coronal loops. The 3-minute umbral oscillations are observed in the transition region, and are then observed to propagate along the sunspot coronal loop system.
These propagating waves are interpreted as the transmission of global p-modes that undergo absorption, slow mode conversion, and are wave-guided into the corona by the strong magnetic field. A complete, simultaneous, view of the atmosphere from the photosphere, chromosphere, transition region and corona is required. |
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