Observational Research of Stratospheric Hydroxyle

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Hydroxide is one of the most important minor constituents in the middle atmosphere because of its high reactivity; however, only a few measurements have been reported so far because of its extremely small abundance. In this research, we succeeded to quantify the stratospheric hydroxyle column by UV spectroscopy to measure A^2SIGMA-X^2II (0,0) band 1P_1, and 3Q_1, absorption lines at 308 nm using the sun as a light source.The measuring system consists of a 1.5 m double-pass grating monochromator, a linear image sensor with a one-stage MCP, a sun-tracker and a 0.5 m telescope, and is set in Hongo campus of the University of Tokyo located at the central Tokyo City. The spectral purity of the system used is 1.2 pm which is a little larger than the Doppler width of the hydroxyle lines. Difficulty comes from the fact that the solar spectrum in this region is filled with solar absorption lines which are much stronger than the terrestrial hydroxyle absorption features. In this research we util … More ized the Doppler shift of the solar spectrum due to the solar rotation in discriminating the terrestrial absorptions from the solar features; this is the most distinctive point of this research. By comparing the solar spectra measured on the east and west edges of the solar disk, it is possible to cancel out the solar structure and make the terrestrial absorption much more prominent.Good data have been obtained since May 1992 after various troubles such as inaccurate sun tracking, insufficient ability of the cooling system, degradation of the optics and temperature drift of the mechanics. The measured hydroxyle vertical columns at noon in summer and winter are 6 x 10^<13> cm^<-2> and 4 x 10^<13> cm^<-2>, respectively, and decreases to 4 x 10^<13> cm^<-2> in the summer evening when the solar zenith angle reaches 60ﾟ. This behavior can roughly be reproduced with a one- dimensional chemical-diffusive model; our understanding of the middle atmosphere photo-chemistry is found to be not far from the truth. Less