Extratropical influence of upper tropospheric water vapor on Greenhouse warmingDespite its small quantity, the importance of upper tropospheric water vapor is its ability to trap the longwave radiation emitted from the Earth's surface, namely the greenhouse effect. The greenhouse effect is defined quantitatively as the difference between the longwave flux emitted by the Earth's surface and the outgoing longwave radiation (OLR) flux emitted from the top of the atmosphere (TOA) (Raval and Ramanathan 1989).