TRMM Radar Observations of Cloud Tops in the Tropical Tropopause Layer

Air dehydrates to stratospheric abundances in the tropical tropopause layer (TTL). The role of overshooting convection in the dehydration process is not well understood. To study this effect, we use the TRMM (Tropical Rainfall Measuring Mission) precipitation radar (PR) to measure the altitudes of cloud tops forming in the TTL. Because the radar signal is dominated by scatter from large particles, these cloud observations imply the presence of strong convective systems with large updraft. Both winter and summer data from two different years are examined to study both interseasonal and interannual variability. The global distribution of these clouds is in good agreement with those of the surface precipitation rates. In addition, the altitude distributions of these clouds follow an exponential dependence. However, clouds over continental regions typically extend to higher altitudes in the tropics. Almost no cloud tops were observed above 20 km. Comparison between the radar cloud tops and colocated IR brightness temperature measurements reveal a large difference in both the diurnal cycle and intensity between continental and oceanic convection.