Pan-Arctic Water Vapour Measurements using the Microwave Humidity Sounder

The Microwave Humidity Sounder (MHS) is an instrument on board the polar orbiting NOAA-18 and MetOp-A satellites. MHS measures the brightness temperatures at five channels near 183 GHz for the purpose of measuring water vapour column without significant interference from clouds. The water vapour retrieval technique is independent of surface emissivity and favours low column amounts of water vapour (< 7 mm), ideal for Arctic winter measurements. A calibration is produced using winter precipitable water measurements from the G-Band radiometer (GVR), located in Barrow, Alaska (71N, 156W). The CANDAC Rayleigh-Mie-Raman lidar (CRL), located in Eureka, Nunavut (80N, 86W) is an eight-channel lidar that measures profiles of cloud and aerosol optical properties, water vapour mixing ratios, and depolarization. A case study shows a thick precipitating ice cloud as seen by the CRL, which extends from the surface to the tropopause. Pan- Arctic plots using the MHS in combination with FLEXPART back trajectories indicate two possible water vapour masses contributing to the formation of the thick ice cloud. The MHS dataset is used to generate Pan-Arctic plots, which can be produced twice-daily with 15 km resolution at nadir. Time evolution of the precipitable water fields can provide insight into the dehydration greenhouse feedback effect. A water budget for the Arctic can also be constructed using the high spatial resolution analysis.