Aerosol microphysical properties, especially their vertical distributions, are important to understand aerosol radiative effects and aerosol-cloud-interactions, which represents the largest uncertainty in future climate projections according to the IPCC report. To make this important information available to the ARM and scientific communities, the CAPI working group proposes to develop an aerosol microphysics profile VAP.
While passive remote sensing can be used to retrieve column-averaged microphysical properties, lidar measurements can provide retrievals of vertically-resolved aerosol microphysical properties. By combining lidar-measured aerosol extinction at both 355 and 532 nm and backscatter at 355, 532, and 1064 nm (3β+2α), it is possible to retrieve profiles of aerosol microphysical properties, such as effective radius and concentration, as shown by Burton et al. (2016) and Ferrare et al. (2017). We plan to use the Tikhonov Advanced Regularization Algorithm (TiARA) developed by the NASA LaRC group, which has been successfully applied in previous studies (Ferrare et al., 2017; Müller et al. 2019), to retrieve vertically-resolved aerosol microphysics. The input data for TiARA will be particle backscatter coefficient profiles at 532 nm and 1064 nm and extinction coefficient profiles at 532 nm from the two-wavelengths high-spectral-resolution lidar (HSRL), as well as particle backscatter and extinction coefficient profiles at 355 nm from the Raman lidar RLPROF-FEX VAP. The retrieved microphysical properties will include aerosol effective radius, number concentration, surface area, volume concentration, and fine-mode fraction.
To implement the VAP, we will start at the ARM Southern Great Plains (SGP) atmospheric observatory in Lamont, Oklahoma. The TiARA algorithm was developed using data from the Combined HSRL and Raman lidar Measurement Study (CHARMS) IOP, which took place from July to September 2015 at SGP. Initially, we will set up and test the retrieval system using CHARMS measurements and compare the results with those of Ferrare et al. (2017) to ensure proper performance of the algorithm. Once the initial implementation and testing are successful, we will apply the retrieval to other time periods when both HSRL and Raman lidar measurements are available, such as during August 2020 to May 2021 at SGP. Additionally, starting in September 2023, ARM plans to deploy AMF3 to the Southeastern US, where collocated HSRL and Raman lidar measurements over forest canopy will provide a good opportunity to apply the TiARA retrieval method.
An implementation plan will be developed and uploaded.
References
Burton, S. P., Chemyakin, E., Liu, X., Knobelspiesse, K., Stamnes, S., Sawamura, P., et al. (2016). Information content and sensitivity of the 3β + 2α lidar measurement system for aerosol microphysical retrievals. Atmospheric Measurement Techniques, 9(11), 5555–5574. https://doi.org/10.5194/amt-9-5555-2016
Ferrare, R., Thorsen, T., Clayton, M., Muller, D., Chemyakin, E., Burton, S., et al. (2017). Vertically Resolved Retrievals of Aerosol Concentrations and Effective Radii from the DOE Combined HSRL and Raman lidar Measurement Study (CHARMS) Merged High-Spectral-Resolution Lidar-Raman Lidar Data Set.
Müller, D., Chemyakin, E., Kolgotin, A., Ferrare, R. A., Hostetler, C. A., & Romanov, A. (2019). Automated, unsupervised inversion of multiwavelength lidar data with TiARA: assessment of retrieval performance of microphysical parameters using simulated data. Applied Optics, 58(18), 4981. https://doi.org/10.1364/ao.58.004981