The Impact of Warm Conveyor Belt Forecast Errors on Variability in the Downstream Waveguide

Atmospheric waveguides denote the location of the jet stream and constrain the motion of Rossby waves. Perturbations of the waveguide can lead to the downstream radiation of Rossby waves, which can often spawn high-impact weather. One hypothesized source of these perturbations is the warm conveyor belt (WCB) of midlatitude cyclones, which transports relatively warm and moist air poleward and upward. The diabatic processes related to this rising motion in the WCB are associated with downstream ridge amplification, which often perturbs the waveguide. Therefore, this study evaluates the potential impact of WCB forecast errors on subsequent downstream waveguide forecasts.

This hypothesis is evaluated for select illustrative North Atlantic case studies during the Northern Hemisphere cool season (October-March) using Model for Prediction Across Scales (MPAS) ensemble forecasts. Lagrangian trajectory analysis will be used to relate the variability in the downstream waveguide to differences in the amplitude and location of WCB trajectories. In addition, ensemble-based sensitivity analysis will be employed to examine the connection between waveguide variability and earlier differences in the vertical profile of relative humidity and temperature within the WCB.