Top: long-term variations in the disk-integrated H₂O volume mixing ratio (blue points), inferred from the HDO measurements at the cloud top from the TEXES data at 7.4 µm. Bottom: long-term variations in the disk-integrated SO₂ volume mixing ratio inferred at the cloud top (7.4 µm, red points). A daily value is shown in this figure. The error bars represent the uncertainty in the disk-integrated HDO and SO₂ volume mixing ratios, averaged over a day. They depend upon the quality of the terrestrial atmospheric transparency, the size of the planetary disk, the continuum level and the number of maps recorded each day. In both cases, the solar activity (measured by the sunspot number) is shown for comparison.