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Search for Travelling Waves
For a pair of wavelengths, λ_{1} and λ_{2}, at a frequency ν, the power curves, P_{λ1(ν)} and P_{λ2(ν)} were created. The cross correlation coefficient, C(Δt, ν), of these power curves as a function of timeshift, Δt, is given by

(83) 
This is used to evaluate the shift in P_{λ2(ν)} which results in maximum correlation with P_{λ1(ν)}. This shift, Δt_{max_corr}, then corresponds to the timelag of P_{λ2(ν)} onto P_{λ1(ν)} at frequency ν, and C(Δt_{max_corr}, ν) is an indication of how good the correlation is. This procedure was then repeated for all frequencies, and between all pairs of wavelengths. From this timelag information, and from a knowledge of the approximate heights of formation (Table 5.1), the speed of possible travelling waves at specific frequencies were calculated (Bocchialini & Baudin 1995; Baudin, Bocchialini, & Koutchmy 1996).
James McAteer
20040114