Altitude resolved ice-fraction in the uppermost tropical troposphere

Artikel i vetenskaplig tidskrift, 2008

The exact nature of the processes responsible for the moistening of the upper tropical troposphere is still uncertain. Altitude resolved measurements of water vapor from Aura/Microwave Limb Sounder (MLS) and cloud ice from CloudSat are used to investigate the ratio of ice mass to total water. Horizontal and vertical ice-fraction distributions in the pressure range 100-316 hPa over the tropical region are presented. They reveal that the ice-fraction is generally low, less than 10% around 316 hPa in general and outside regions of deep convection in the altitude levels above. On the other hand, the ice-fraction can be significant at higher altitudes in large regions above deep convection, reaching values of ∼90%. Below the tropical tropopause layer (TTL) ice and water vapor distributions have similar spatial patterns indicating that water in both phases is transported up to the upper troposphere by the same processes. Over regions of strong deep convection where ice is transported into the TTL, the dissimilar patterns of ice and water vapor could be interpreted as that the cloud ice gives a limited final moistening effect. Copyright 2008 by the American Geophysical Union.