The North Atlantic jet stream is a major feature of the global atmospheric circulation and plays a key role in the development of weather systems hitting Europe. Typically, the jet stream is strongest at about 10 km altitude but is very variable in strength, latitude and shape. When the jet is oriented straight across the Atlantic (from west to east) it can be exceptionally strong, sometimes exceeding 200 mph. However, often it is wavy, meandering in latitude by thousands of km and it may even split into two distinct jet structures at different latitudes.
Forecast busts over Europe have been related to particular Rossby wave configurations 5-6 days beforehand when there is a trough over the Rockies and a ridge of warm, moist air extending over eastern North America with embedded convective systems. The hypothesis driving the North Atlantic Waveguide and Downstream Impacts Experiment (2016) was that perturbations to the jet stream over North America and west Atlantic, particularly associated with diabatic processes, propagate along the jet stream and grow, leading to large differences in possible flow weather situations downstream. The aircraft experiment set out to observe the jet stream structure and processes perturbing it. In this talk I will focus on the mechanisms through which diabatic processes can influence the jet stream structure, Rossby waves and their development coupling with cyclones and anticyclones. The role of diabatic influence on jet stream predictability is examined.
John Methven’s research utilises new observations and models to develop and test theories of atmospheric dynamics. He led the UK component of the North Atlantic Waveguide and Downstream Impacts Experiment, NAWDEX (in 2016) and this summer led the Arctic Summertime Cyclones field campaign, based in the Norwegian Arctic investigating the interaction between cyclones and sea ice. In tropical meteorology, he is involved in several projects on the fundamental influences of large-scale wave dynamics on tropical weather systems and high impact weather.
Professor Methven is co-chief editor of the Quarterly Journal of the Royal Meteorological Society. He is co-chair of the World Meteorological Organization’s working group on Predictability Dynamics and Ensemble Forecasting (PDEF).