SPARC Water Vapor Assessment II: intercomparison of satellite and ground-based microwave instruments


As part of the SPARC (Stratosphere-troposphere Processes And their Role in Climate) water vapour assessment (WAVAS-II), satellite measurements taken from, or coincident with, seven sites from which ground-based microwave instruments measured water vapor in the middle atmosphere.  Six of the ground-based instruments are part of the Network for the Detection of Atmospheric Composition Change (NDACC) and provide datasets which can be used for drift and trend assessment.   Measurements from these ground-based instruments were compared with satellite datasets that have provided retrievals of water vapor in the lower mesosphere over extended periods since 1996. 

Water vapor timeseries were compared just above the stratopause (0.46 hPa).  Most of the datasets started in, or after, 2004, and showed annual increases in H2O of 0-1%/year.  In particular, MLS showed a trend of between 0.5%/year and 0.7%/year at the comparison sites.  However the two longest measurement datasets, NDACC measurements dating back to 1996, show much smaller trends of +0.1%/year (at Mauna Loa, Hawaii) and -0.1%/year (at Lauder, New Zealand).  The results were published in Atmospheric Chemistry and Physics, and are available at