Chapter 5

Oscillations in Multi-Wavelength Optical Observations of the Quiet-Sun Network

Oscillations in Network Bright Points (NBPs) are studied at a variety of chromospheric heights. In particular, the three-dimensional variation of NBP oscillations is studied using image segmentation and cross-correlation analysis between images taken in the light of Ca II K₃, Hα core, Mg I b₂, and Mg I b₁-0.4 Å. Wavelet analysis is used to isolate wave-packets in time, and to search for height-dependent time delays which result from upward- or downward- directed travelling waves. In each NBP studied, evidence is found for kink mode waves (1.3 mHz, 1.9 mHz), travelling up through the chromosphere and coupling with sausage mode waves (2.6 mHz, 3.8 mHz). This provides a means for depositing energy in the upper chromosphere. Other upward- and downward- propagating waves in the 1.3-4.6 mHz range are also found. Some oscillations do not correspond to travelling waves and we attribute these to waves generated in neighbouring regions.