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Computing E(k) at lower resolution or with certain algorithms introduces a roll off (reduced energy) and high frequencies. Since the behavior of the spectra, especially the rolloff starting around wave number 200 is of most interest, this should be avoided.
Using “PG2” output (cyan curve below) is not recommended - this is most likely due to the downscaling downsampling of the velocity when transforming from the dynamics to the PG2 physics grid, removing energy from small scales.
“intbilin” algorithm is not recommended (brow and green curves below). This algorithm is very nice for analysis, but does remove energy from small scales. “bilin” is a little better (orange, blue)
Best results are obtained by the highorder algorithm (GLL 2048HO and GLL 3072HO).
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