Y. Tohjima et al., DISTRIBUTION OF TROPOSPHERIC METHANE OVER SIBERIA IN JULY 1993, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 102(D21), 1997, pp. 25371-25382
Airborne observations of atmospheric methane (CH4) mixing ratio were c
arried out over Siberia during July 15-30, 1993, using a continuous me
asurement system. The distribution of CH4 in the upper troposphere at
an altitude of about 7 km was highly variable (1.72-1.91 parts per mil
lion, or ppm), being affected by intrusion of stratospheric air, long-
range transport of CH4 from the source region, and a synoptic-scale mi
xing process. During flights along nearly constant latitude between Ya
kutsk (62.10 degrees N, 129.50 degrees E) and Nizhnevartovsk (60.57 de
grees N, 76.40 degrees E) on July 19 and 28 we observed large-scale en
hancements of CH4 from near 90 degrees to 100 degrees E with a horizon
tal scale of more than 500 km. Accompanied by high humidity and low mi
xing ratios of CO2 and O-3, the air masses with enhanced CH4 mixing ra
tio were considered to be affected by lower tropospheric air. The prob
able source region of the CH4 was inferred to be the West Siberian Low
land, which contains vast wetlands and huge oil/gas fields. The distri
bution of CH4 in the lower troposphere (0.1-3 km) over the boreal wetl
ands in the West Siberian Lowland, ranging from 1.85 ppm to 2.75 ppm,
showed large accumulations near the ground in the morning. The shortte
rm temporal variations in the vertical profile of CH4 mixing ratio rev
ealed that the accumulated CH4 was transported to the free troposphere
with the growth of the mixed layer. On the other hand, the distributi
on of CH4 (0.1-1 km) over the tundra areas in the Siberian Arctic was
less variable (1.81-1.84 ppm), and little accumulation was observed.