A dual perspective on cloud-aerosol-radiation interaction using novel polarimetric and hyper-spectral measurements
Final Report Abstract
The goal of the project was to advance our understanding on cloud-aerosol-interaction processes, which are important for more accurate climate and weather prediction. The number of activated cloud condensation nuclei (CCN) is a key quantity to study these processes. Therefore we proposed to observe this quantity using two different strategies. The first (PhD project 1) was to measure the aerosol optical properties between the clouds using ground-based polarimetric observations from which CCN can be derived. For this purpose the SSARA sun and sky photometer has been equipped with polarizer filters to measure linearly polarized light at 501.5 nm. Accurate novel radiometric and polarimetric calibration methods have been developed. Further a new algorithm to derive aerosol microphysical properties has been developed that autoamatically selects the data points in between clouds in partly cloudy scenes. In order to test the accuracy of the retrieval algorithm, it has been applied on synthetic observations, which were generated with a 3D Monte-Carlo radiative transfer model. Afterwards the algorithm was applied on SSARA observations taken during the A-LIFE field campaign and the aerosol optical thickness as well as other aerosol microphysical properties were retrieved in regions between clouds. The second approach (PhD project 2) was to derive CCN from vertical profiles of cloud microphysical properties retrieved from hyperspectral observations of solar radiation reflected from cloud sides. Here we got the opportunity to fly the foreseen instrument on the HALO aircraft which allowed us to obtain much better data since the viewing geometry from above is much less subject to shadows and obstructions by other clouds. The spectral camara system specMACS has been adapted for airborne observations of cloud sides and was operated on the HALO research aircraft during the campaigns ACRIDICON-CHUVA NARVAL-II and NAWDEX. Algorithms to retrieve droplet phase and particle size from those observations have been developed, which rely on accurate georeferenciation of the measurements and cloud and illumination geometry. The georeferenciation and also cloud motion information was gained with unprecedented accuracy from stereographic evaluation of cloud imagery on the aircraft. A comparison of retrieved droplet size profiles to a cloud resolving aerosol-chemistry model and cloud in-situ data allowed for in-depth analysis of the cloud-aerosol interaction and for a test of the hypothesized derivation of the CCN from an observed droplet size profile.
Publications
- (2020) The challenge of simulating the sensitivity of the Amazonian cloud microstructure to cloud condensation nuclei number concentrations. Atmos. Chem. Phys. (Atmospheric Chemistry and Physics) 20 (3) 1591–1605
Polonik, Pascal; Knote, Christoph; Zinner, Tobias; Ewald, Florian; Kölling, Tobias; Mayer, Bernhard; Andreae, Meinrat O.; Jurkat-Witschas, Tina; Klimach, Thomas; Mahnke, Christoph; Molleker, Sergej; Pöhlker, Christopher; Pöhlker, Mira L.; Pöschl, Ulrich;
(See online at https://doi.org/10.5194/acp-20-1591-2020) - 2019, Aircraft-based stereographic reconstruction of 3-D cloud geometry, Atmos. Meas. Tech., 12, 1155-1166
T. Kölling, T. Zinner, B. Mayer
(See online at https://doi.org/10.5194/amt-12-1155-2019) - 2019, Remote Sensing of Cloud Droplet Radius Profiles using solar reflectance from cloud sides. Part I: Retrieval development and characterization, Atmos. Meas. Tech., 12, 1183-1206
Ewald, F., T. Zinner, T. Kölling, B. Mayer
(See online at https://doi.org/10.5194/amt-12-1183-2019) - Retrieval of aerosol properties from ground-based polarimetric sky-radiance measurements under cloudy conditions. J. Quant. Spectrosc. Radiat. Transfer, 228:57-72, 2019
H. Grob, C. Emde, and B. Mayer
(See online at https://doi.org/10.1016/j.jqsrt.2019.02.025) - The polarized sun and sky radiometer SSARA: design, calibration, and application for ground based aerosol remote sensing, Atmos. Meas. Tech. Discussions, 2019
H. Grob, C. Emde, M. Wiegner, M. Seefeldner, and B. Mayer
(See online at https://doi.org/10.5194/amt-2019-226)
