PhD Thesis: Information Content of Halo Displays for Remote Sensing of Ice Crystal Properties.
Advisors: Prof. Dr. Bernhard Mayer, LMU Munich and Prof. Dr. Markus Rapp, DLR Oberpfaffenhofen, Germany.
Cirrus clouds, consisting of small non-spherical ice crystals, cover about 30% of the globe and play an important role in the Earth’s energy budget. Depending on the radiative properties of their components, cirrus clouds can have either a cooling or warming effect on the Earth's atmosphere and surface. The radiative properties and thus the amount of transmitted and reflected sunlight is mainly governed by ice crystal shape, surface roughness, and orientation. This thesis presents a novel method to retrieve these ice crystal properties using ground-based camera observations of halo displays.
Halo displays form by refraction and reflection of sunlight by ice crystals and, depending on their microphysical properties, exhibit unique patterns of bright and often colorful features in the sky. More info about halo displays:
Examples for halo displays recorded with HaloCam. Left to right, top to bottom: 22° halo, 22° parhelion (sundog), 22° halo with upper and lower tangent arcs, 22° halo with circumscribed halo.
This research project is a joint collaboration between LMU Munich and Caltech/NASA JPL and is funded by the European Union’s Framework Programme for Research and Innovation Horizon 2020 under the Marie Skłodowska-Curie Grant Agreement No. 754388 and from LMU Munich’s Institutional Strategy LMUexcellent within the framework of the German Excellence Initiative (No. ZUK22).
Water clouds are an important component of the Earth's energy balance as they reflect incoming shortwave solar radiation and absorb and re-emit longwave thermal radiation. According to the IPCC AR5 (Clouds and Aerosols), clouds still contribute one of the largest uncertainties to estimates of the Earth’s energy budget. Investigating cloud properties is therefore an essential step towards a better understanding of their role in our climate. Current retrievals of cloud optical thickness and effective particle size using passive satellite imagers are based on 1D radiative transfer theory. As such, they work well only for horizontally homogeneous clouds but fail for convective clouds with 3D morphology.
Cloud tomography is a promising approach for treating clouds as 3D objects. Multi-angle observations from passive imagers are used to recover the 3D volume of the cloud's optical and microphysical properties. While the method has been successfully demonstrated for airborne observations, more efficient methods are required for larger cloud volumes. This is important to advance the method to global observations of multi-angle satellite imagers. Volumetric cloud reconstruction is a large inverse problem and is solved iteratively by comparing the observations to forward simulations from a 3D radiative transfer solver until convergence. Within this project we investigate new ways to increase the efficiency of the tromographic cloud reconstruction.
Teaching assistant: "Clouds: Microphysics and Convection" (SS/2013, WS/2013, SS/2014, WS2014, SS/2015, WS/2015)
The lecture teaches the basics of cloud formation from the micro to the macro scale. Topics covered in the microphysics part are phase diagrams, droplet formation, condensation, coalescence, precipitation, aerosol direct and indirect effects, global electric circuit, thundercloud charging, and lightning. The convection part teaches about instability criteria, generation of convection, thunderstorm classification, tornadoes, outflow, downdrafts, mesoscale convective systems, observations and forecasting.