On the role of the vertical velocity profile in the tropical tropopause on cold point formation

The effect of the observed decrease of the vertical velocity with height in the tropical tropopause layer on the formation of the cold point has been investigated, using a very simple model of the approximate balance between vertical temperature advection and radiative heating. The modeled large-scale and monthly-mean temperature profile has a cold point not only if the radiative equilibrium temperature increases with height, which is the usual explanation for the cold point, but also if the vertical velocity decreases with height. If in the model the vertical velocity is assumed to decrease with height as observed, and other parameters, particularly the radiative equilibrium temperature, are fixed, then the modeled cold point height and temperature are close to the observations. This suggests that the observed decrease of the vertical velocity with height in the tropical tropopause layer plays an important role in the formation of the cold point.