Stratospheric Nudging And Predictable Surface Impacts (SNAPSI): A protocol for investigating the role of stratospheric polar vortex disturbances in subseasonal to seasonal forecasts

Based on a set of controlled, subseasonal ensemble forecasts of three recent events, the protocol aims to address four main scientific goals. First, to quantify the impact of improved stratospheric forecasts on near-surface forecast skill. Second, to attribute specific extreme events to stratospheric variability.

Third, to assess the mechanisms by which the stratosphere influences the troposphere in the forecast models. Fourth, to investigate the wave processes that lead to the stratospheric anomalies themselves. Although not a primary focus, the experiments are furthermore expected to shed light on coupling between the tropical stratosphere and troposphere.

The output requested will allow for a more detailed, process-based community analysis than has been possible with existing databases of subseasonal forecasts.