Abstract. Following on from the previous efforts of INTERACT (INTERcomparison of Aerosol and Cloud Tracking),
15the INTERACT-II campaign used multi-wavelength Raman lidar measurements to assess the performance of an automatic compact micro-pulse lidar (MiniMPL) and two ceilometers (CL51 and CS135), respectively, to provide reliable information about optical and geometric atmospheric aerosol properties. The campaign took place at the CNR-IMAA Atmospheric Observatory (760 m asl, 40.60° N, 15.72° E), in the framework of the ACTRIS-2 (Aerosol Clouds Trace gases Research InfraStructure) H2020 project. Co-located simultaneous measurements involving a MiniMPL, two 20 ceilometers, and two EARLINET multi-wavelength Raman lidars (MUSA and PEARL) were performed from July to December 2016. Range-corrected signals (RCS) of MiniMPL showed an average difference with respect to MUSA/PEARL RCS of less than 10-15% below 3.0 km above sea level, largely due to the use of an inaccurate overlap correction, and smaller than 5 % in the free troposphere. For the CL51, the average difference with respect to MUSA/PEARL attenuated backscatter is <20-30 % below 3 km, larger above. The variability of the CL51 calibration 25 constant is within ±30 %. For the CS135, the performance is similar to the CL51 in the region below 2.0 km asl, while in the region above 3 km asl the differences are ±40 %. The variability of the CS135 normalization constant is within ±40-50 %.Finally, following up to the outcome of a few specific tests performed during the campaign using the CHM15k ceilometer, the CHM15k historical dataset available at CIAO from 2010 to 2016 were investigated to evaluate potential effect of the 30 ceilometer laser fluctuations on calibration stability. The time series of the laser pulses shows an average variability of 10 % with respect to the nominal power which conforms to the specification. Nevertheless, laser pulses variability follows seasonal behavior with an increase in the number of laser pulses in summer and a decrease in winter. This may partly explain the dependency of the ceilometer calibration constant on the environmental temperature hypothesized during INTERACT.
35