History of Satellite Observations of East Pacific Atmospheric Rivers

From the winter quarters of the Lewis and Clark expedition at Fort Clatsop on the Oregon coast in 1805, Meriwether Lewis remarked on the dismal coastal weather: "The rain continues, with Tremendious gusts of wind, which is Tremendious…. This kind of weather lasted all day,… Certainly one of the worst days that ever was!". Undoubtedly the Corps of Discovery became well-aquainted with heavy rainfall originating from atmospheric rivers.

The terms “Atmospheric River” or “Tropospheric River” were not used in refereed literature until the 1990’s, although earlier works hinted at the existence of narrow corridors of moisture transport. With the advent of satellite observations in the 1960’s, meteorologists began to discover the fingerprints of these phenomena via cloud observations. Early geostationary satellites depicted “cloud rivers” or “pipeline cirrus” impacting the U.S. west coast.

Routine use of passive microwave imagery to retrieve total column water vapor began in the late 1980’s with the launch of the Special Sensor Microwave / Imager instrument, whose descendants continue to provide realtime monitoring of atmospheric rivers today. Passive microwave data opened the door to quantitative studies of atmospheric rivers, by providing the water vapor measurements needed to compute integrated moisture flux. In recent years, dedicated coastal observatories, global water vapor data sets, cloud radars, and satellite sounding systems have begun to probe the 4-dimensional moisture structure of atmospheric rivers.

The timeline of our understanding of atmospheric rivers will be presented from the standpoint of evolving satellite observing systems.