David Whiteman wrote:
I believe there is consensus that the measurements that cannot currently be made within the specifications of GCOS-112 using any technology include water vapor mixing ratio. Because of that, I believe it is important for this group to specify what intermediate measurement specifications might be useful for assessing climate change while work continues on developing sensors that can meet the GCOS-112 specification.
For example, at the workshop Reinhout Boers presented results that showed the anticipated increases in water vapor over the Netherlands during the next century. An international consortium of climate models has been used to look at the same thing. The results seem to indicate that in general the largest percentage increases in water vapor concentration are anticipated to occur at ~ the 200 mb level with smaller increases both lower and higher in the atmosphere. This implies that trend monitoring of water vapor would be most efficient if sensors were capable of quality measurements at the 200 mb level or approximately 12 km agl. What is the required precision/accuracy required to reveal trends at this level? Again Reinhout presented a framework for determining this using the trend detection work of Weatherhead et. al. (1998). I suggest that this could be an approach for developing a useful set of intermediate measurement specifications for GRUAN. There are several technologies that currently supply quality measurements at the 200 mb level and they include CFH, corrected RS92 and Raman lidar (at night). Perhaps a careful study along the lines described above would indicate that one or more of these technologies is currently able to provide measurements useful for monitoring anticipated trends in water vapor. If GRUAN can develop specifications that can currently be met and that are of sufficient quality to reveal anticipated trends in water vapor, I think it will be in a much stronger position for advocating for resources to support its implementation.