Evolution of tropical deep-convective clouds derived from ground-based imaging spectroradiometer measurements

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Specifically the project will derive the vertical profile of microphysical properties of tropical deep-convective clouds (DCC) from ground-based measurements of reflected radiation from cloud sides by an imaging spectroradiometer system. This general objective is to characterize the vertical evolution of DCCs, which play an important role in the Earths climate system. The evolution will be studied with respect to the impact of aerosol and thermodynamic conditions on the cloud particle growth. The planned measurements will be performed on the new Amazonian Tall Tower Observatory (ATTO), of 320 m height situated in the Amazon Basin near the equator. ATTO is equipped with instruments to measure micrometeorological and atmospheric chemical variables, as well as aerosol properties. It provides ideal observation conditions with clear seasons (wet and dry season), and daily occurrence of DCCs in a highly variable environment with respect to concentrations and types of aerosol particles. The new imaging spectroradiometer system, SPIRAS (SPectral Imaging Radiation System), will be used to derive vertical profiles of thermodynamic phase and cloud effective radius with high temporal and spatial resolution by means of adapted methods based on three-dimensional radiative transfer simulations. In this way vertical zones characterizing the droplet growth (diffusion, coalescence, mixed-phase, and glaciation) will be identified. Auxiliary measurements by an infrared camera and a scanning depolarization Lidar will be used to estimate the height and the temperature of the observed cloud element. Additionally, polarization measurements by Lidar will support the retrieval of the thermodynamic phase which is important to identify the phase transition. By means of the data obtained we will validate assumptions (effective particle radius as conservative cloud property) of retrieval methods for satellite-based observations to derive microphysical profiles.