A backscatter lidar forward operator for aerosol-representing atmospheric chemistry models

• Main Author: Geisinger, Armin
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Hohenheim 2020
• Subjects: Vulkanasche; Lidar; Aerosol; Luftfahrt; Eyjafjallajökull; Atmosphäre; Modell; Vorwärtsoperator; Ceilometernetzwerk; Validierung; Streueigenschaften; Forwardoperator; Ceilometernetwork; validation; scattering properties; Physics
• Online Access: http://nbn-resolving.de/urn:nbn:de:bsz:100-opus-17542; http://opus.uni-hohenheim.de/volltexte/2020/1754/

State-of-the-art atmospheric chemistry models are capable of simulating the transport and evolution of aerosols and trace gases but there is a lack of reliable methods for model validation and data assimilation. Networks of automated ceilometer lidars (ACLs) could be used to fill this gap. These networks are already used for the detection of clouds and aerosols, providing a 3D dataset of atmospheric backscatter profiles. But as the aerosol number concentration cannot be obtained from the ACL data alone; one needs a backscatter-lidar forward model to simulate lidar profiles from the model variables. Such an operator allows then for a qualitative and quantitative model validation based on ACL data. In this work, a newly developed backscatter-lidar forward operator and the related sensitivity studies are presented and results of the forward operator applied on model output data are compared to measured ACL profiles in the frame of a case study. As case study, the eruption of the Icelandic volcano Eyjafjallajökull in 2010 was chosen and extensively analyzed. The Consortium for Small-scale Modeling - Aerosols and Reactive Trace gases (COSMO-ART) model of DWD (Deutscher Wetterdienst) was operated during this event for ash-transport simulations over Europe. For the forward model, the attenuated backscatter coefficient is used as lidar-independent variable, which only relies on the laser wavelength. To calculate the attenuated backscatter coefficient, the size-dependent aerosol number concentration and the scattering properties of each aerosol type and size have to be simulated. While the aerosol number concentration is a model output variable, the scattering properties were determined by extensive scattering calculations. As these scattering calculations require assumptions about the aerosol refractive indices and shapes, sensitivity studies were performed to estimate the uncertainties related to the particle properties as represented by the model system. An analysis of the particle shape effect for the extinction and ...