Satellite Sounder Observations of Contrasting Tropospheric Moisture Transport Regimes: Saharan Air Layers, Hadley Cells, and Atmospheric Rivers
Water vapor controls how clouds and precipitation form, but its vertical distribution in the atmosphere can vary significantly under different conditions in the Earth’s lowest atmospheric layer, called the troposphere. Researchers compared satellite-derived data of vertical atmospheric moisture profiles with co-located radiosonde (an instrument package carried by weather balloons) observations obtained during ocean-based intensive field campaigns to show how well satellite sounders can detect and measure tropospheric moisture features. The ability to use satellite data to effectively measure water vapor profiles is important for near-real-time forecasting in data-sparse regions.
Water vapor is a key element of the global water cycle. The heat released when water vapor condenses is a primary driver of global atmospheric circulation, and the precipitation produced when water vapor converts to clouds and raindrops supports life and human activities. Demonstrating the capability of a satellite sounder to monitor the vertical moisture profiles under varied and extreme conditions is a key step in establishing the use of satellite moisture profiles in forecasting and climate studies.
This research, performed by a team of researchers including a scientist at the U.S. Department of Energy’s (DOE) Pacific Northwest National Laboratory (PNNL), examined the performance of satellite sounder atmospheric vertical moisture profiles under varied and extreme tropospheric conditions. Three such conditions — the Atlantic Ocean Saharan air layers (SALs), the tropical Hadley cells, and the Pacific Ocean atmospheric rivers (ARs) — encompass contrasting moisture profiles driven by different heat transport mechanisms. Researchers assessed the effectiveness of operational satellite sounder moisture profiles retrieved from the infrared and microwave sounders on board the National Oceanic and Atmospheric Administration (NOAA) Joint Polar Satellite System (JPSS) using co-located dedicated radiosonde observations from the NOAA Aerosols and Ocean Science Expeditions (AEROSE) in 2013 and the CalWater/Atmospheric Radiation Measurement (ARM) Cloud Aerosol Precipitation Experiment (ACAPEX) in 2015, both on board the NOAA ship Ronald H. Brown. The processes that transfer energy and water in the SALs, Hadley cells, and ARs result in vertical gradient discontinuities and persistent uniform clouds, aerosols, and precipitation that present challenges to satellite sounding. The research demonstrated that the operational satellite sounder 100-layer moisture profile product has accuracy that is within the uncertainty requirements. In both the AEROSE and CalWater/ACAPEX environments, the sounder-derived moisture data showed the ability to detect and resolve important tropospheric moisture features, demonstrating a near-real-time forecast usefulness over data-sparse regions.