VERTICAL COLUMN ABUNDANCES OF HCN DEDUCED FROM GROUND-BASED INFRARED SOLAR SPECTRA - LONG-TERM TREND AND VARIABILITY

A set of high-resolution IR solar spectra recorded at the International Scientific Station of the Jungfraujoch, Switzerland, from 84/06 to 93/06, and at the National Solar Observatory McMath-Pierce solar telescope facility on Kitt Peak, Arizona, U.S.A. from 78/05 to 92/07 have been analyzed to determine the vertical column abundances of hydrogen cyanide, HCN, above the two stations. The analysis was based on least-squares curve fitting of calculated spectra to the observations encompassing the P4 and the P8 lines of HCN respectively located at 3299.5273 and 3287.2483 cm(-1). The results obtained for the two stations indicate that no significant long-term trend affects either of the two databases; however, this analysis reveals variable increases during springtime of up to a factor of 2 in the HCN total column above the Jungfraujoch and even up to 3 above Kitt Peak. The calculated mean vertical column abundances, excluding the spring observations, are equal to (2.55 +/- 0.30) x 10(15) molec./cm(2) (S.D.) and (2.75 +/- 0.30) x 10(15) molec./cm(2) respectively above the Jungfraujoch and the Kitt Peak observatories. Based on a realistic volume mixing ratio profile, these columns translate into mean volume mixing ratios equal to 190 x 10(-12) ppv at the respective altitudes of the stations.