A Comparison of HALOE/UARS Derived Methane Profiles With Balloon Measurements

Measurements of various minor constituents from a tropical location in India (Hyderabad; 17.5N, 78.6E) has been started 1987 using the balloon-borne cryosampler technique and gas chromatography based laboratory analysis. In the period of 1987 to 1998, four balloon flights have been conducted on (1) March 27, 1987, (2) April 9, 1990, (3) April 16, 1994, and (4) April 18, 1998. The vertical distribution of CH₄ are constructed in the altitude range of about 8 to 37 km by GC-FID analysis and calibrated against the Linde/NIST calibration gases. The 1987, 1994 and 1998 profiles are overall in agreement (except a small kink) with each other as well as with the MPIC 2D model simulations, whereas that for 1990 deviates significantly in 25-32 km altitude range. We have estimated the HALOE CH₄ vertical profiles by averaging all the available data between 16⁰N-19⁰ latitude in March-April of every year. To obtain values at particular altitude the HALOE profiles (Level 2 data, SPF formatted) were first interpolated. The basic characteristics of the CH₄ profiles from balloon-borne and HALOE measurements are fairly in agreement on overlapping time period. It is also apparent from the HALOE data that the interannual variations of CH₄ at most stratospheric altitude has the strong stratospheric QBO signal. Satellite data show that in the easterly phase of QBO the enhanced mixing rate near the sub-tropical 'surf' zone lower the CH₄ concentration around 30 km, where the QBO intensity peaks. This was the situation in March-April 1990 and 1997. Thus the 1990 balloon profile closely matches with the 1997 HALOE CH₄. However, it should be pointed out that the satellite based vertical profiles are rather smooth compared to the in-situ observations. This smoothing could be caused by the algorithm used in the vertical profile estimation from the radiation spectra. Detailed results and features will be discussed during the presentation.