Column abundance of atmospheric CH4 and precipitable water measurements from ground-based infrared solar spectra

摘要

Abstract: IR solar spectra were measured automatically by an IR solar spectrometer (ISS) capable of 0.4 cm$+$MIN@1$/ resolution. Good signal-o-noise ratio (SNR) and relatively high resolution made it possible to select unsaturated, temperature insensitive intervals for a specific absorption gas with minimal overlap by other interfering gases. In the wavelength range of 3.410-3.438 $mu@m, the absorption is mainly due to atmospheric methane and water vapor. A line- by-line computation method was used to calculate theoretical atmospheric absorption. By adjusting the total column density to obtain an exact agreement between the calculated and observed absorption, the total column density of atmospheric methane and water vapor were obtained. In the paper, some result observed by ISS for more than one year were reported. Since the April of 1997, we have been monitoring the column abundances of atmospheric CH$-4$/ and H$-2$/O continually on every clear cloudless day with the method indicated above. The result show that CH$-4$/ has little variation in one day, but has considerable seasonal variation. More than one high density peaks were found, two of which occurred in hot summer and cold winter, and the smallest value was found in spring. The reason is explained as emissions of local sources and atmospheric transport. The precipitation of column water vapor has a largely variation even in one day, the smallest precipitation appeared in winter, the biggest value was found in hot summer, seasonal variation could be as large as 40 times. !9