Secular trend of the methane absorption bands: variation in the absorption band depth for the bands at 0.73 μm (top panel) and 0.89 μm (middle panel) compared with the secular variation for the band at 1.72 μm (bottom panel) from G13. Lines in green represent a sinusoidal fit of band depths from this work; lines in purple represent a sinusoidal fit of band depths from Grundy & Fink (1996). The points in the gray shadow represent replicate values (at longitude 360°) to better visualize the variation in the shifts with the longitude.