Fig. 4

Analysis for the longitude wave components of h_mM₂, N_mM₂, and H_n. a shows longitude variation of the △h_mM₂ at 64°N. The gray dots are gridded △h_mM₂; the solid line is the Fourier fitting; the dashed lines indicate the corresponding 1-σ error. b presents latitude variations of the 1-σ errors of △h_mM₂, △N_mM₂, and △H_n fittings. c is latitudinally averaged amplitudes of the longitude wave − 1 to − 6 in △h_mM₂, △N_mM₂, and △H_n