A quasi‐permeable barrier in the equatorial lower stratosphere

Analyses of global isentropic maps of potential vorticity from the United Kingdom Meteorological Office data assimilation system reveal that there is a region of strong meridional potential vorticity gradients in the equatorial lower stratosphere. A semi‐Lagrangian tracer transport model is used to show that this region of strong PV gradients acts as a quasi‐permeable barrier to cross‐equator mass exchange on isentropic surfaces.