Aerosol-Cloud Interaction using multiple ground based remote sensing instruments and in urban regions

Aerosol-Cloud Interaction using multiple ground based remote sensing instruments and in urban regions Zaw Han, Yonghua Wu, Barry Gross, Fred Moshary, and Samir Ahmed NOAA CREST, The City College of New York, New York, NY 10031, USA The interaction between aerosol particles and cloud plays an important role in studies of climate radiation. In particular, it is generally assumed that increases in aerosol loading results in higher concentration of cloud condensation nuclei which ultimately lead to increase cloud droplet number concentration and smaller cloud droplets effective radius. In this paper, direct ground based method is used to assess the Aerosol-Cloud Interaction at City College of New York (CCNY) based on the synergistic measurements by using microwave radiometer (MWR), multi filter rotating shadow band radiometer (MFRSR), light detection and ranging (LIDAR) systems, and Santa Barbara Discrete Ordinate Radiative Transfer (SBDART) model. The SBDART model is used to create the look-up-table for atmospheric transmittance which will then be used with MWR and MFRSR data. MFRSR provides transmittance, MWR gives liquid water path (LWP) and LIDAR offers aerosol extinction nearby clouds. The measured transmittance and LWP are function of cloud optical depth (COD) and cloud droplet effective radius (Reff). A method of iterative inversion algorithm is developed to obtain the COD and Reff. Then, aerosol extinction and cloud Reff are acquired to evaluate the correlation between them. In this task, we combine the use of our Microwave Radiometer and the Multi-filter Rotating Shadow-band Radiometer to provide simultaneous aerosol and cloud properties that can be used to explore Aerosol Cloud Interactions. The general nature of the algorithm can be seen from the flow chart for the Retrieval of Reff and τcod. The measurement data from MFRSR and MWR are used to obtain the cloud optical depth and cloud effective radius based on the flow chart below. An example of the retrievals as well as how the cloud effective radius decreases with enhanced aerosol extinction coefficient is seen for the case of May 13, 2013. The extinction coefficient is obtained from a Raman LIDAR near the cloud base. The aerosol cloud interaction parameter is defined as Aerosol Cloud Index (ACI) or Indirect Effect (IE) equation. In figure 5(a), we plot the results for all days. The best fit we have obtained is ACI ~ 0.3 which is at the high end of the literature but still within reasonable theoretical bounds.