Scattered ultraviolet radiation in the upper stratosphere 1: Observations

Abstract

Observations of scattered solar near‐UV radiation in the upper stratosphere were obtained during a 1983 balloon flight at 31°N latitude. The instrument design was patterned after the UV ozone spectrometer on board the Solar Mesosphere Explorer satellite. The measurements cover the wavelength range 175 to 325 nm at a spectral resolution of 1.5 nm, spanning a range of viewing elevation angles from −3.3° to 14.6° with a field of view 1.65×10−5 sr. Observations began at midday near 46 km and continued to approximately 1700 LT near an altitude of 40 km. Calibrated radiances reported here are determined from the raw data using measured sensitivity characteristics of the spectrometer. A correction to account for the polarized nature of Rayleigh‐scattered radiation is included which employs the measured polarization response of the instrument and assumes single scattering of solar radiation. The single pass spectrometer was susceptible to a small but in some cases important contamination by stray light. This effect is quantified using observations obtained at low altitudes and low solar elevation angles, i.e., large optical paths. The uncertainty in radiances is determined by statistical and systematic errors (efficiency, polarization, and stray light determinations) and ranges typically from 15 to 30%. In contrast to previous observations, scattered radiances decrease rapidly at wavelengths shortward of 210 nm.