Speaker
Description
During the twilight event the boundary between the illuminated and shadowed parts of the atmosphere shifts upward with the increasing solar zenith angle. This makes it possible to retrieve the vertical profile of aerosol extinction from the ground – based measurements of the twilight sky brightness as a function of the solar zenith angle, performed in a narrow field of view and a narrow spectral range.
The twilight sky brightness measurements were carried out in Georgia, South Caucasus and Belgium in the periods after the Pinatubo eruption in 1991 as well as Nabro, 2011 and Raikoke, 2019 eruptions. The extinction profiles retrieved from selected measurements illustrate the capability of the method. The Levenberg-Marquardt retrieval algorithm with the forward model based on the fully spherical Monte Carlo code Siro (developed in FMI) was used for the retrieval. Beside of the stratospheric aerosols, aerosol extinction enhancements in the troposphere were observed during a few saharan dust transport events.
Further development of the experimental equipment and the retrieval method will be discussed. Some advantages of observing twilight phenomena from satellites, especially for ALTIUS, will be considered.
