Recent changes in methane mixing ratio and its ¹³C content observed in the southwest Pacific region

Figures & data

Figure 1. Time series of MR, August 1989 to August 2009 (upper panel: NOAA04 scale), and δ¹³C, December 1987 to April 2009 (lower panel: VPDB scale) for methane measured at Baring Head, New Zealand. Data series (blue circles) are decomposed into trend (red) and seasonality (green) as described in the text. Tick marks on the abscissas denote 1 January of the particular year.

Figure 2. Daily mean tropospheric-average CH₄ dry air mole fraction (TAMF) retrieved from NIR solar absorption spectra acquired by Fourier Transform Infrared Spectrometry at Lauder, compared with gas chromatographic analysis of flask samples from Baring Head. The Lauder TAMF dataset has yet to be calibrated, which is expected to account for the mean offset between the datasets.

Figure 3. Screened hourly mean surface CH₄ MR (15:00 h–16:00 h local time, |u| > 6 m s⁻¹) representative of regional scales derived from continuous closed-cell FTS measurements at Lauder, New Zealand, compared with flask samples from Baring Head analyzed by gas chromatography.

Table 1. Growth rate by calendar-year (ppb year⁻¹).

Calendar year	Baring Head	Lauder (tropospheric column)
2005	(−2.6) 0.2 (2.6)	(0.4) 1.6 (2.5)
2006	(0.8) 1.6 (2.4)	(−3.9) 1.7 (4.7)
2007	(3.6) 6.3 (7.9)	(4.6) 8.9 (12.1)
2008	(2.5) 4.2 (8.5)	(−0.1) 4.1 (6.6)
Each entry is the median of 12 monthly differences between consecutive years centered on 1 January (July–July to June–June) of monthly mean data at each site. The preceding and succeeding values in parentheses are the first and third quartiles of the ranked 12 differences.