Examination of hygroscopic properties of aerosols using a combined multiwavelength elastic-Raman lidar

Water vapor is an important greenhouse gas due to its high concentration in the atmosphere (parts per thousand) and its interaction with tropospheric aerosols particles. The upward convection of water vapor and aerosols due to intense heating of the ground leads to aggregation of water particles or ice on aerosols in the air forming different types of clouds at various altitudes. The condensation of water vapor on aerosols is affecting their size, shape, refractive index and chemical composition. The warming or cooling effect of the clouds hence formed are both possible depending on the cloud location, cover, composition and structure. The effect of these clouds on radiative global forcing and therefore on the short and long term global climate is of high interest in the scientific world. A major interest is manifested in obtaining accurate vertical water vapor profiles simultaneously with aerosol extinction and backscatter in the meteorological and remote sensing fields all around the globe in an effort to understand the hygroscopic properties of aerosols. In previous work, simultaneous measurements of RH with backscatter measurements from a surface nephelometer were used to probe the hygroscopic properties of aerosols. However, most of these measurements were not able to probe the high RH domain since such high RH is rare for surface altitudes. For this reason, experiments using a 355nm raman water vapor and aerosol lidar at the ARM site were used. Capable of providing simultaneous backscatter and RH profiles, and performing the experiments under low altitude cloud decks insured stable well mixed layers as well as probing RH profiles to above 95% which is required for the differentiation of different aerosol hygroscopic models.