Behavior of NO2 and O3 columns during the eclipse of February 26, 1998, as measured by visible spectroscopy

Abstract

Observations of the NO2 and O3 columns using zenith-viewing differential absorption spectroscopy in the visible range (450–540 nm) were carried out at Izaña Observatory (Tenerife, 28°N, 16°W, 2370 m above sea level.) during the eclipse of February 26, 1998 (95% occultation over the station). Ozone has been retrieved using two different spectral ranges to minimize the effect of the continuous change of the solar spectrum shape as the Sun is being occulted. Small variations before the maximum phase in agreement with previous observations are found, but because of the change in the shape of the solar spectrum, it cannot conclusively be determined whether the ozone changes are real or due to interferences with changing Fraunhofer lines. The difficulties in observing small changes of absorbing gases during solar eclipse when using remote sensing technique that uses the solar UV and visible radiation as the source are discussed. NO2 displays an increase in phase with the degree of solar occultation, as compared to a non eclipse day of 1.55±0.09. A simple model assuming that changes over short times scales are only due to changes in photodissociation, using O3 and temperatures obtained from an ozone sounding station close to the observatory, reproduces the observed variation when the NO2 bulk is assumed to be at an altitude of 28 km. Correction for differences between local solar zenith angle (SZA) and the SZA where the absorption takes place is taken into account.