CloudSat shedding new light on high-reaching tropical deep convection observed with Meteosat

Characteristics of warmer water vapor pixels (WWVPs) defined by brightness temperature difference (Delta TB) between 6.2 mu m and 10.8 mu m channel of Meteosat-8 greater than zero were examined using collocated CloudSat data during the period from 15 October to 15 November 2006 over tropical Africa. On the basis of CloudSat we provide a physical interpretation of Delta TB > 0. It is found that WWVPs occur in deep convective areas where cloud tops are in the tropical tropopause layer above 14 km. It is also found that the relationship between 10.8 mm TB and DTB is generally linear and WWVPs are frequent with very cold cloud top temperatures lower than the cold-point tropopause temperature. These findings suggest that WWVPs are explained by the contrast between colder background of 10.8 mu m TB associated with overshooting tropical deep convection and warmer water vapor channel temperature due to the emission from water vapor lines in the warmer stratosphere above.