Raman lidar measurements of aerosol distribution and cloud properties

Abstract

Measurements obtained by the PSU Lidar Atmospheric Profile Sensor (LAPS) Raman lidar, during different periods, provide a comprehensive dataset to characterize cloud properties and aerosol distributions. The PSU Raman lidar measures the profiles of molecular nitrogen, molecular oxygen and the rotational Raman scatter (the mixture of all molecular species) at both visible and ultraviolet wavelengths, which are then used to generate vertical aerosol extinction profiles from the incremental extinction. Since the optical extinction at different wavelengths is strongly dependent on the size distribution of aerosols, variations in the profile of the size distribution can be inferred over an interesting range corresponding to accumulation mode particles, 50 nm to 1µm. The variation in the extinction profiles at different wavelengths is also used along with the water vapor profiles to observe the formation, growth and dissipation of cloud structures. The water vapor concentrations have been seen to decrease in regions surrounding a growing cloud as the particles increase in size by absorbing the water. Also, the water vapor concentration is found to increase as clouds begin to dissipate. The change in the size of the cloud particles during the different stages can also be observed in the multi-wavelength aerosol extinction. Results obtained from different locations, and for a wide range of atmospheric conditions, are used to compare and contrast the aerosol distributions and also to study the physical properties of clouds.

Aerosol optical properties observed by combined Raman‐elastic backscatter lidar in winter 2009 in Pearl River Delta, south China

“…This would explain the low SSA values on 27 and 28 November as due to a larger proportion of internally or externally mixed BC in absorbing aerosols in the PRD. The different SSA in the moderate pollution period (0.92 ± 0.03) can be explained by the differences in aerosol and combustion types [Verghese et al, 2005]. The low-absorption (high SSA) profiles obtained are mainly from urban/industrial aerosol, which mainly consist of nonabsorbing particles [Dubovik et al, 2002].…”

Lidar investigations of atmospheric dynamics

“…We expect that it will be possible to quantify both the number density of the liquid and ice particles by combining the Raman lidar measurements and the aerosol size information obtained by using the polarization ratio of the scattering phase function. The measurements of the physical properties of clouds and studies of their evolution during growth and dissipation should help in better understanding the radiative forcing that is still of much concern in climate change studies 20,21 . The many different properties that can be simultaneously measured using a Raman lidar make it a most valuable tool for these investigations, and the three measurements that are most useful in studying the dynamical processes are the profile sequences of water vapor, aerosol optical extinction and temperature.…”

“…Daytime convection, weather front motion, undular bore waves, and evolution processes of clouds are important features that are studied with Raman lidar 19 . The microphysical thermodynamic processes that result in cloud formation can be studied using Raman lidar measurements of temperature and water vapor distribution surrounding cloud formations 20,21 . Changes in aerosol particle size are observed using multi-wavelength measurements of optical extinction profiles 20-28 .…”

“…Aerosol optical extinction at UV and VIS wavelengths of several clouds moving through the vertical lidar beam show the changes in the size distribution of particles in and around the clouds20,21,42 .…”