Workshop: Stratospheric predictability and impact on the troposphere

On sub-seasonal timescales, coupling between the stratosphere and troposphere represents a significant source of skill for northern mid and high-latitudes. Previous studies have examined this skill either on a case-by-case basis or from the perspective of the additional skill present during sudden stratospheric warming (SSW) or strong polar vortex events. Here we complement these approaches by...

This study investigates the influence of atmospheric initial conditions on winter seasonal forecasts of the North Atlantic Oscillation (NAO). Hindcast (or reforecast) experiments – which differ only in their initial conditions – are performed over the period 1960–2009, using prescribed sea surface temperature (SST) and sea‐ice boundary conditions. The first experiment (“ERA‐40/Int IC”) is...

Several recent studies have suggested that the stratosphere can be a source of subseasonal-to-seasonal predictability of Southern Hemisphere circulation during the austral spring and early summer seasons, through its influence on the eddy-driven jet. We exploit the large sample size afforded by the hindcasts from the European Centre for Medium-Range Weather Forecasts Integrated Forecast System...

Early ideas on the dynamics of stratosphere-troposphere coupling involved planetary-waves directly coupling both regions. However, recent work has largely focused on coupling via the zonal-mean flow as observed during Stratospheric Sudden Warmings (SSWs). Here, the dynamics of planetary-wave coupling is revisited in the context of extreme positive and negative wave-1 stratospheric heat flux...

Sudden stratospheric warming (SSW) events significantly disrupt the stratospheric circulation, and are a major mode of subseasonal variability in the winter atmosphere. Major SSWs appear as dramatic polar-cap warmings of 20K or more, accompanied by weakening of the circumpolar zonal wind and reversal from the normal westerly to easterly wind. SSW anomalies can develop rapidly over days,...