Variation of Fourier transform values with height in different period (frequency) ranges as marked with different colours. Dotted lines are observed decrease with height whereas continuous lines are fit applied to obtain dissipation lengths, as per Eq. (6), using full height range (left panel), and in two height ranges (0–10 Mm and 10–70 Mm, right panel). The obtained dissipation lengths in two different height ranges are summarised in Table 1.