Should we call them 'Atmospheric Rivers?'

Atmospheric rivers (ARs) are long, narrow bands of water vapor that transport moisture from one place to another. They can deliver much-needed rain or snow, but if they’re too intense, they can cause flooding, landslides and power outages in the western U.S. and elsewhere. A new study utilizes an intensity scale for atmospheric rivers, akin to the hurricane scale, to rank them from AR-1 to AR-5 (with AR-5 being the most intense). This scale can help determine whether an atmospheric river will bring benefit or cause chaos and is helping meteorologists and city planners better understand the societal impacts of these events.

An atmospheric river is typically formed when warm temperatures create moist packets of air, which strong winds then transport across the ocean. The intensity scale ranks these atmospheric rivers based on how long they last and how much moisture they transport. As a result, some West Coast weather outlets are using the intensity scale to help communities know whether an atmospheric river will bring benefit or cause chaos.

The atmospheric river that contributed to disastrous flooding in Pakistan was an AR-5, the most damaging, most intense atmospheric river rating.
This underscores the need to know when these events are coming and how to prepare for them. To this end, F. Martin Ralph, an atmospheric scientist at Scripps Institution of Oceanography, and his colleagues developed the scale for the U.S. West Coast and the new study demonstrates that atmospheric river events can be directly compared globally using it.

The researchers also found that more intense atmospheric rivers (AR-4 and AR-5) are less common than weaker events, with AR-5 events occurring only once every two to three years when globally averaged. The most intense atmospheric rivers are also less likely to make landfall, and when they do, they are unlikely to maintain their strength for long and penetrate farther inland.

The study identified four “centers,” or hotspots, of where AR-5s tend to die, in the extratropical North Pacific and Atlantic, Southeast Pacific, and Southeast Atlantic. Cities on the coasts within these hotspots, such as San Francisco and Lisbon, are most likely to see intense AR-5s make landfall. Additionally, the study found that strong El Niño years are more likely to have more atmospheric rivers, and stronger ones at that.

The authors hope to see, within five years or so, meteorologists on TV around the world incorporating the atmospheric river intensity scale into their forecasts, telling people whether the atmospheric river will be beneficial or if they need to prepare for a serious storm. By better understanding the impacts of atmospheric rivers, we can prepare and mitigate the damage they can cause.

This study is published with open access and is freely available:

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[aurorad]

I think it should be categorized. W/ climate instability, we will likely see periods of nothing to a series of "atmospheric rivers "