Direct Impacts of Waves on Cold-Point Tropopause Temperature

Waves in the tropical tropopause layer (TTL) play important roles in controlling water vapor transport into the stratosphere. Equatorial waves are partially responsible for driving tropical upwelling as a tropical part of the Brewer-Dobson circulation. The tropical upwelling induces adiabatic cooling in the TTL, which removes water vapor more effectively from air entering the stratosphere by freeze-drying. Here we show an additional importance of waves using observational data: waves lower cold-point tropopause temperature regardless of any changes in mean upwelling. This is because a cold-point is more sensitive to the cold phase of a wave than the warm phase, so the net effect of temperature fluctuations due to waves makes the cold-point colder than without waves. While radiosonde measurements provide high vertical resolution at limited locations, GPS data provide global observations. Using the two data sets, we show tropical cold-point tropopause temperature and lower stratospheric water vapor are significantly modulated by the existence of waves in the TTL. We further show that this direct wave impact is not well represented in reanalysis data due to weaker waves and coarse vertical resolution in models.