GROUND-BASED FTIR MEASUREMENTS WITH HIGH TEMPORAL RESOLUTION

We outline how ground-based Fourier transform infrared (FTIR) measurem ents of stratospheric trace species, obtained with high temporal resol ution, could be used to detect filaments of polar vortex air at mid-la titudes and therefore test high spatial resolution chemical transport models (CTMs). Vertical column abundances of HCl, ClONO2, HNO3, N2O an d HF have been obtained from FTIR solar absorption measurements made t hroughout the day from Aberdeen, UK (57 degrees N, 2 degrees W) on sev eral days during winter/spring 1993/94 and 1994/95. The short-timescal e (similar to 2 hours) variability observed in the columns is attribut ed to real atmospheric variations and is often associated with the pas sage of high latitude air over Aberdeen. This is confirmed by 3D model ling studies which qualitatively reproduce and rationalise the observe d changes in the column data on January 19 1994, January 20 1995 and F ebruary 26 1995. We describe the viewing geometry of ground-based FTIR measurements and we suggest a measurement strategy which should maxim ise the information retrieved on horizontal gradients in stratospheric trace species columns from FTIR measurements.