First validation of satellite microwave liquid water path with ship-based observations in marine low clouds

Abstract:

We present the first validation study of satellite microwave liquid water path, from four operational sensors, against in-situ observations from a ship-borne three-channel microwave radiometer collected over the northeast Pacific during May-August of 2013, along a ship transect length of 40˚ (33.7˚N, 118.2˚W - 21.3˚N, 157.8˚W). The satellite sensors analyzed here are: The Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI), Special Sensor Microwave Imager/Sounder (SSMIS) on the Defense Meteorological Satellite Program F16 and F17 satellites, and The Advanced Microwave Scanning Radiometer (AMSR-2) on board the Global Change Observation Mission – Water (GCOM-W1). Satellite retrievals show an overall correlation with hourly-averaged in-situ observations of 0.86 and a positive bias of 10.0 gm², which decreases to 1.0 gm² and a correlation that increases to 0.91 when selecting overcast scenes. The satellite bias for broken scenes remains below 22.2 gm², although the removal of clear-sky in-situ samples yields an unbiased relationship. Satellites produce a diurnal cycle with amplitudes (35-47 gm²) consistent with ship-based observations. Longitudinal biases remain below 17.4 gm², and they are negligible in overcast scenes and when clear-sky samples are removed from the in-situ hourly average. Our study indicates that satellite microwave retrievals are a reliable dataset for climate studies in marine warm low clouds. The implications for satellite visible/infrared retrievals will be also discussed.