Definitions

[uncool]

Is a "-pause" a boundary or a boundary layer? For example, is the magetopause the boundary between where the Earth's magnetic field dominates and where the solar influence dominates, or is it the boundary layer between the two? Similarly, is the heliopause a boundary or a boundary layer (i.e. does it have thickness)?

=Uncool-

[D H]

It's a boundary layer, and a somewhat arbitrary one. You aren't going to be able to find a spot above the Earth where 1 nanometer below you can say "that's the troposphere!" and one nanometer above, "that's the stratosphere!" (i.e., the tropopause). All of these -pauses are a bit fuzzy, a bit arbitrary, and shift with time. They are very useful concepts, but don't take them as gospel.

[J.C.MacSwell]

It's a boundary layer, and a somewhat arbitrary one. You aren't going to be able to find a spot above the Earth where 1 nanometer below you can say "that's the troposphere!" and one nanometer above, "that's the stratosphere!" (i.e., the tropopause). All of these -pauses are a bit fuzzy, a bit arbitrary, and shift with time. They are very useful concepts, but don't take them as gospel.

 

I would not call that a boundary layer. I would still interpret that as a boundary. In the usual sense boundary layers have a defined thickness, even if that thickness is somewhat arbitrary, shifting, or fuzzy, and the character of that thickness is essentially different from what lies outside of it.