Particle tracking in turbulent environments

Three dimensional Particle Tracking Velocimetry is a well-known experimental method for the Lagrangian measurements of fluid flows. It has been developed independently in many groups, mainly because of its intuitiveness and conceptual simplicity. The tracer particles need to be detected in the multi-view videos and through the three-dimensional calibration and matching between different views to be registered in the 3D space and time. The next obvious step is the so-called tracking, that links 3D clouds of particles between the frames in time, solving an assignment problem. Despite the simplicity of the concept, the technical details are important and need to be translated into a working computer software solution. We will present one of the existing solutions, abbreviated OpenPTV which is an open source software (http://www.openptv.net). We will work through the details of the 3D-PTV, focusing on turbulence and Lagrangian turbulence statistics. We will also demonstrate and make a hands- on tutorial of the test case, providing the pre- and post-processing toolset to get to the Lagrangian turbulence statistics such as a second order Lagrangian structure function or pair dispersion analysis.

LES of clouds and its application to weather and climate model improvement

Predicting where and when clouds form is notoriously difficult. Clouds are small compared to, for example, depressions and fronts, which makes it difficult to represent them in numerical weather prediction models. Moreover, we need to know about the behaviour of water droplets, snow and ice. Only over the last two decades, we have been able to explicitly represent the clouds responsible for e.g. thunderstorms in a crude way in weather models. Taking into account the effect of smaller clouds, which play a key role in climate sensitivity, remains hard. Large-Eddy Simulation (LES) provides a way to study the behaviour of both cumulus clouds and cloud decks in detail.

This seminar will cover:

• Introduction to clouds species and thermodynamics (potential temperature, virtual potential temperature, phase changes and conserved variables)
• Models of the atmosphere: global models, explicit convection (grey zone) and large-eddy simulation.
• Cloud-resolving LES: subgrid dynamics and DNS/Moist Parcel-in-Cell approaches.
• LES-diagnostics and cloud organisation.
• Boundary conditions (e.g. coupling with land surface) and other forcings.
• Microphysics, aerosols and radiation in LES.
• Validation of LES and the importance of fieldwork (including the upcoming EUREC4A-UK campaign)

Workshop on structure identification in cloudy environments

We work through identifying and categorising coherent boundary layer structures in Large-Eddy Simulation output from large (GBs) simulations of moist shallow convection under varying ambient conditions. The workshop will demonstrate the usage of python (specifically xarray and luigi) to construct data analysis pipelines where every step in a data analysis process (extracting fields, compositing, running external Fortran and C++ programs and producing analysis plots) can be executed with a single command from the command line. The workshop will use analysis software produced as part of the GENESIS project (http://homepages.see.leeds.ac.uk/~earlcd/GENESIS/) as a case study and detail how this software can be used to study coherent structures in other applications.