F. Erle et al., ON THE INFLUENCE OF TROPOSPHERIC CLOUDS ON ZENITH-SCATTERED-LIGHT MEASUREMENTS OF STRATOSPHERIC SPECIES, Geophysical research letters, 22(20), 1995, pp. 2725-2728
Examples for the influence of tropospheric clouds on the ground-based
measurement of stratospheric species using the DOAS-technique (Differe
ntial Optical Absorption Spectroscopy) are reported. At Camborne/Great
Britain (50.216 degrees N, 5.316 degrees W) on Sept. 11 - 15, 1994, e
pisodic enhancement of absorption lines of O-4, H2O, O-3 and NO2 were
observed in coincidence with tropospheric clouds being in the instrume
ntal field of view (1.1 degrees full angle). At a solar zenith angle (
SZA) of 88 degrees, absorption enhancements up to roughly a factor of
3 were detected for the tropospheric species O-4 and H2O and the tropo
spheric fractions of the total column of O-3 and NO2. The additional a
bsorptions in the visible spectral range are probably caused by multip
le Mie-scattering in tropospheric clouds. For our conditions, a tropos
pheric light path enhancement (TLPE) of 135+/-40 km can be inferred, b
eing largely independent of SZA. This observation has several importan
t implications for the atmospheric radiative transport, which are brie
fly discussed.