Standardizing the determination of the molecular backscatter coefficient profiles for LALINET lidar stations using ERA-Interim Reanalysis

Abstract

The molecular backscatter signal is necessary in aerosol lidars to determine the aerosol backscatter and extinction. It is derived using atmospheric temperature and pressure profiles from simultaneous soundings or climatological values from radiosonde measurements. In cases when no radiosonde measurements are available at or near the lidar stations the U.S. Standard Atmosphere is commonly used. Although the atmospheric reanalysis can also be used to obtain the atmospheric temperature and pressure profiles at any station, we found no reports of its use for this purpose. Therefore, the goal of this research is to compare molecular backscatter coefficients derived from radiosonde measurements with ones derived using the ERA-Interim reanalysis and the U.S. Standard Atmosphere 1976 (USSA-1976), for the locations of the lidar stations from the Latin America Lidar Network (LALINET). The differences between radiosonde measurements and ERA-Interim temperature profiles are smaller than the differences between radiosonde measurements and the USSA-1976 temperature profiles. In many stations, the differences between the temperature in radiosonde measurements and ERA-Interim are smaller than 2 K and the greatest differences are about 4 K. However, the differences between temperature in radiosonde measurements and in the USSA-1976 are smaller than 10 K only in three stations, and the greatest differences are about 20 K. The profiles of relative differences of the molecular backscatter coefficients between radiosonde measurements and ERA-Interim show negative values at most of the pressure levels. Positive values greater than 0.5 % are only observed above 8 km. However, the profiles of relative differences of the molecular backscatter coefficients between radiosonde measurements and the USSA-1976 shows positive values from surface to 12 km in all stations. Only in four stations are observed negative differences above 14 km with values smaller than -5 %. Comodoro Rivadavia presents the best behavior because is located near to 45 degree of latitude, but even in this station the differences between radiosonde measurements and the USSA-1976 are bigger than those observed between radiosonde measurements and ERA-Interim.