Ground‐based microwave measurements of water vapor from the midstratosphere to the mesosphere

We present 5 months of retrievals from a new Water Vapor Millimeter‐wave Spectrometer (WVMS) instrument that has been deployed at Table Mountain, California (34.4°N, 242.3°E). The single most important improvement over previous WVMS instruments is that instead of a set of 90 filters, this instrument has a fast Fourier transform spectrometer that provides 16,384 channels across 500 MHz, with a channel bandwidth of ∼30 kHz. The additional information provided by this spectrometer makes it possible to extend the altitude range of the WVMS measurements from the current ∼40–80 km range to ∼26–80 km. We present details of the retrieval scheme and study the effects on the retrieved profiles of fitting instrumental baseline components. We compare the retrievals to coincident measurements from the NASA Aura Microwave Limb Sounder (MLS) instrument with a particular emphasis on understanding the stability of the 26 km retrievals. While the retrieval is sensitive to variations at this altitude, neither the MLS‐retrieved water vapor mixing ratios nor those retrieved by WVMS show much variation over the 5 month period: a good indication of the stability of both instruments.