Weather and the Jetstream - predicting severe weather events

The importance of the jet stream for our weather is often remarked upon by television and radio presenters, and indeed its behaviour is of central importance to weather forecasting. Modern weather forecast models simulate the atmosphere with tremendous detail, far more than is needed to represent the jet stream. Nevertheless, forecasts of the jet stream diverge from reality in a systematic way over the course of a few days – the model jet undulates less than the real one, and the problem worsens as the forecast goes on. We do not know why models all exhibit this failing, and it can sometimes lead to ‘forecast busts’ or a failure to predict a severe weather event a few days ahead.

To find out why the source of this problem, a major international experiment led by German research aircraft is being conducted in the autumn of 2016. The experiment, called NAWDEX (North Atlantic Waveguide and Downstream Impacts Experiment) will involve detailed measurements of the jet stream in the eastern and mid Atlantic with the aircraft, together with downstream ground-based measurements over Europe. The aim is to relate the measured structure of the jet stream over the Atlantic both to air entering it over North America and to the weather that develops downstream over Europe. The National Centre for Atmospheric Science (NCAS) and the Met Office are joining forces to provide the UK element of the downstream measurements. This consists of flights of the FAAM aircraft and a ground-based programme, centred around the UK mesosphere-stratosphere-troposphere radar and lidar facility at Capel Dewi near Aberystwyth. There is also an extensive campaign of radiosonde launches at Capel Dewi and other sites around the UK.

The student will begin by examining the aircraft and ground-based data to build a detailed picture of the jet stream as it passed over the UK during selected events. This picture will be related to the measurements made by German and French aircraft flying upstream out of Iceland, to determine how much the structure of the jet stream changes along its length. New techniques will need to be developed to analyse the radar and lidar data to give the best picture.
The project will then move on to model case studies that occur during the campaign using the Weather and Forecasting (WRF) model, to determine the link between disturbances at jet stream level and the weather that develops over Europe. By understanding how well the model represents the actual jet stream, this work will evaluate how much error in forecasts over Europe can be attributed to the inability to properly model the jet stream.

This project is a great opportunity for the interested student to receive a diverse education in handling specialist atmospheric measurements, state-of-the-art numerical modelling, and theory, all while contributing to a major international field research project.