Is there an extratropical tropopause layer?

There has been increasing recent interest in the Tropical Tropoapuse Layer, which is the layer separating tropical air with tropospheric characteristics below from stratospheric air above. In the extratropics, there is also a distinct layer of that separates air with characteristically low values of tropospheric stability from air with higher stratospheric stability. Using US high vertical resolution radiosonde data, we show that the thickness of this layer increases monotonically from a thickness of about 1 km at 30 0N to about 3-4 km poleward of about 50 0N. Furthermore, we demonstrate that conventional radiosonde data can also be used to show the same relationship, even with its lower vertical resolution. We will explore how the thickness of this Extratropical Tropopause Layer varies during baroclinic mixing events and relate these results to theories of the extratropical tropopause.