Upper-tropospheric water vapor and the SR

Water vapor in the upper troposphere is a key greenhouse agent and an important quantity in climate feedbacks. There is a link between lightning activity and this water vapor: deep convection, which produces lightning, simultaneously lifts moisture into the upper layers of the troposphere. Lightning activity thus correlates with the content of water vapor in the upper troposphere.

Because the SR is proportional to global lightning activity, the resonances can in principle be used as an indirect proxy for upper-tropospheric water vapor too — that is, for a quantity that is otherwise difficult to measure globally and continuously. This extends the climatic usefulness of the SR beyond temperature alone.

This is an indirect, multi-stage link (temperature and convection → lightning → SR; simultaneously convection → moisture), so any quantitative interpretation is sensitive to the same limitations as the other climatic proxies from the SR (see #56). For this reason we present the topic as a hypothesis in active research, not as a verified measurement method.