A3 - Model error and uncertainty for midlatitude cyclones analyzed using campaign data
Principal Investigator: Prof. Dr. George C. Craig
In this project, data from a transatlantic measurement campaign will be used to investigate how processes such as the release of latent heat in clouds modify the atmospheric wave pattern. This upscale effect is crucial for the predictability of weather, but difficult to characterize because of the huge range of scales involved. The use of data from a field campaign especially designed to observe these processes, with multiple aircraft and state of the art remote sensing instruments, will provide an unprecedented window into the dynamics of upscale growth, and provide an essential ground truth for related projects in W2W that make use of routine observations and numerical models.
In particular, the three-dimensional structure of synoptic-scale waves over the North Atlantic and the influence of triggering features related to diabatic processes are investigated based on a comprehensive and unprecedented data set that will be observed during NAWDEX (North Atlantic Waveguide and Downstream Impact Experiment) in 2016. In the midlatitudes, forecast skill of high impact weather is often linked to the correct representation of the waveguide, i.e., the strong potential vorticity (PV) gradient on isentropic surfaces collocated with the jet stream. It is expected that diabatic processes related to different dynamic systems, such as warm conveyor belts (WCBs) associated with extratropical cyclones or tropical systems transitioning in the extratropics, interact with the waveguide. Inadequately reproduced diabatic processes can cause systematic errors in the waveguide. The internationally coordinated field experiment NAWDEX aims at investigating triggering mechanisms of the midlatitude waveguide, the evolution of Rossby waves along the waveguide and the downstream impact of diabatically modified PV anomalies.
This project will identify systematic errors in the representation of the waveguide in NWP models and their relation to diabatic processes. Based on a multitude of remote sensing and in-situ observations the three-dimensional structure of the waveguide and the interaction with diabatic systems will be characterized. Errors of the waveguide will be manifested as errors in the PV distribution. The first-time deployment of a wind lidar and a microwave temperature profiler onboard an aircraft allows to develop a new method to derive PV from collocated wind and temperature observations. By comparing the observations and analysis fields, initial condition errors in relation to diabatic processes will be evaluated. In collaboration with Project A7 the predictability of the NAWDEX cases and their relation to diabatic processes will be studied.
The PhD student will work on the subproject "Assessment of model errors in warm conveyor belts and their impact on downstream dynamics":
Diabatic processes in warm conveyor belts and their insufficient representation in numerical models are seen as a major source of forecast errors. The NAWDEX campaign is expected to provide unique measurements in these important regions that will be assimilated in operational numerical weather forecasting models. The influence of such observations on the weather evolution downstream through parallel data assimilation and forecasting experiments with the new global model ICON of Deutscher Wetterdienst and potentially another global modelling system will be investigated.