The NOAA coastal atmospheric river observatory

Atmospheric rivers (ARs) are narrow bands of enhanced water vapor transport often found in the warm sector of extratropical cyclones that form over the oceans or that entrain moisture from oceanic regions. They are responsible for about 95% of the global meridional moisture transport and they can cause extensive flooding when they strike land. Polar-orbiting satellite sensors (e.g., SSM/I, AMSU-E) provide adequate measurements of the water vapor in ARs, but the winds that drive the moisture transport are not measured adequately. In addition, once ARs reach land, the satellite methods no longer work. Scientists at NOAA's Earth System Research Laboratory have been studying ARs impacting the West Coast of the United States since the late 1990's. Through this research, they have developed the concept of an AR observatory (ARO). As applied in NOAA's Hydrometeorological Testbed, the ARO consists of an observing couplet: a coastal site where water vapor transport is measured and an inland site, usually located along the nearest inland terrain barrier, where the precipitation that falls is enhanced by orographic forcing. The coastal site contains a Doppler wind profiling radar, a global positioning system (GPS) receiver, and a surface meteorological tower. The inland site contains a vertically pointing S-band precipitation profiler, a raindrop disdrometer, and a surface meteorological tower. This paper will describe the ARO in more detail, demonstrate some of the hydrometeorological applications that have been developed using the ARO, and report on some of the key scientific findings that have resulted from ARO research.