QBO and QTO of atmospheric methane

The 12-month running means of methane (CH4) concentrations at the surface/lower troposphere averaged for latitude groups 1–8 (1, 82–63°N; 2, 56–53°N; 3, 47–36°N; 4, 32–26°N; 5, 20–13°N; 6, 5–14°S, 7, 41°S only; 8, 65–90°S) showed oscillations but the peak spacings were similar to that of 30 mb wind (∼30 months) only for groups 3, 4 and 7. A cross-correlation with 30 mb wind showed maximum good correlations (+0.7) with a phase lag of about 6 months for CH4 in group 7 (in agreement with Camp et al. [2001. The sensitivity of tropospheric CH4 to the interannual variability in stratospheric ozone. Chemosphere-Global Change Science 3, 147–156]) and about 12 months for CH4 in groups 6 (+0.7). A spectral analysis indicated for 30 mb wind, a prominent Quasi-biennial oscillation (QBO) at 2.34 years and a minor peak at 2.06 years. For Southern Oscillation Index (SOI) (T−D), there was a prominent Quasi-triennial oscillation (QTO) peak at 3.6 years, but there was also a less prominent but significant QBO at 2.54 years. All CH4 groups showed significant QBOs in the range 2.22–2.58 years but also showed more prominent QTOs in the range 3.2–4.1 years, and barely significant peaks in the range 1.6–1.9 years (19–22 months). To test the ozone mechanism proposed by Hamilton and Fan [2000. Effects of the stratospheric QBO on long-lived greenhouse gases in the troposphere. Journal of Geophysical Research 105, 20581–20587] (stratospheric wind QBO affecting stratospheric ozone, in turn affecting the filtered UV, the tropospheric OH radical, and finally tropospheric CH4), TOMS-SBUV data were analyzed. Many CH4 and ozone groups showed QBOs in the range 2.22–2.77 years, and lower periodicities in the range 1.60–1.91 years (19–22 months [Tung, K.K., Yang, H., 1994. Global QBO in circulation and ozone. Part I. Reexamination of observational evidence. Journal of Atmospheric Science 51, 2699–2707]), confirming that the ozone mechanism was operative. A disconcerting feature is the QTO of ∼3.5 years, which was present in CH4 in all latitude groups, but in ozone, only in groups 3, 6, 7.