Atmospheric river

An atmospheric river (AR) is a narrow corridor or filament of concentrated moisture in the atmosphere. Other names for this phenomenon are tropical plume, tropical connection, moisture plume, water vapor surge, and cloud band. Atmospheric rivers consist of narrow bands of enhanced water vapor transport, typically along the boundaries between large areas of divergent surface air flow, including some frontal zones in association with extratropical cyclones that form over the oceans. Pineapple Express storms are the most commonly represented and recognized type of atmospheric rivers; the name is due to the warm water vapor plumes originating over the Hawaiian tropics that follow various paths towards western North America, arriving at latitudes from California and the Pacific Northwest to British Columbia and even southeast Alaska. In some parts of the world, changes in atmospheric humidity and heat caused by climate change are expected to increase the intensity and frequency of extreme weather and flood events caused by atmospheric rivers. This is expected to be especially prominent in the Western United States and Canada. The term was originally coined by researchers Reginald Newell and Yong Zhu of the Massachusetts Institute of Technology in the early 1990s to reflect the narrowness of the moisture plumes involved. Atmospheric rivers are typically several thousand kilometers long and only a few hundred kilometers wide, and a single one can carry a greater flux of water than Earth's largest river, the Amazon River. There are typically 3–5 of these narrow plumes present within a hemisphere at any given time. These have been increasing in intensity slightly over the past century. In the current research field of atmospheric rivers, the length and width factors described above in conjunction with an integrated water vapor depth greater than 2.0 cm are used as standards to categorize atmospheric river events.