Why is the troposphere 8km higher at the equator than the poles? Fundamentals of atmospheric modeling show that the height of the tropopause depends on the location, notably the latitude, and that the troposphere is roughly 8km higher at the equator than the poles depending on the time of year.

First guess was that the temperature of the would impact its density (for example, here's the data for -50° and 50° c) - though this does not appear to show the cause of why is the troposphere 8km higher at the equator than the poles.

Why is the troposphere 8km higher at the equator than the poles?
To start with a definition, the tropopause is the boundary between troposphere and stratosphere; within the troposphere temperature decreases with increase in altitude (the temperature profile is dominated by radiative heat from the Earth's surface), whereas in the stratosphere temperature increases with altitude (the temperature profile is dominated by solar radiation).

Increases in troposphere temperature are associated with increase in tropopause height. Factors in play include the amount of water vapour being evaporated from equatorial seas; interannual variations in tropopause height can result from both local and large-scale driving forces. The tropopause responds to the average temperature of the entire underlying layer: this is higher at the equator and lower at the poles.