Abstract
The temperature structure of the tropical troposphere resembles a moist adiabat, with a lapse-rate transition toward dry adiabatic where water becomes scarce at an altitude H-ma similar to 8 km (350 hPa). Infrared emission by water vapour cools a deeper layer, extending up to H-rad similar to 14 km (160 hPa). Five consequences of these unequal heights are reviewed.
1. Upper-tropospheric relative humidity is often low, highly variable, and bimodal, due to the rapidity of drying by radiative subsidence.
2. Large-scale divergent circulations (e.g. equatorial v wind) exhibit a two-celled vertical structure, with an elevated convergence layer near 8-10 km in the rising branch.
3. The dominant deep convective heating process chances from latent heating at low levels to eddy heat-flux convergence in the upper troposphere. This requires a substantial updraught-environment temperature difference, which leads to large entrainment near H-ma, yielding stratiform anvil clouds which also contribute radiative heating.
4. The rising, branches of deep (similar toH(rad)) vertical circulations export more heat than they import as moisture, so that large-scale tropical dynamics can be characterized by a 'gross moist stability'.
5. Divergent motions with a vertical wavelength similar to8 km, corresponding to Kelvin or gravity wave speeds of similar to 15 m s(-1), are excited by simple (e.g. uniform) heating profiles extending through the lapse-rate change near H-ma.