Water vapor of the polar middle atmosphere: Annual variation and summer mesosphere conditions as observed by ground-based microwave spectroscopy

We have been operating a ground-based microwave radiometer for the 22.235 G Hz water vapor line at the ALOMAR observatory, Norway, in 1995/96 and conti nuously since July 1997. Its high latitude location (69 degrees N, 16 degre es E) provides a new and unique dataset of stratospheric and mesospheric wa ter vapor observations. We briefly describe our instrument and measuring te chnique and present the data of our ongoing measurements. The water vapor m ixing ratio shows a pronounced annual cycle that is stronger than what has been reported for mid-latitudes. We also present an analysis of our data fo r the upper mesosphere for the relationships between mesospheric water vapo r, temperature, polar mesosphere summer echoes (PMSE), and noctilucent clou ds (NLC) during summer months. This investigation indicates that water vapo r is already present near mesopause heights when the PMSE/NLC season starts and is still present long after it has declined.