In the crosshairs of an atmospheric river
Ned Rozell
907-474-7468
March 17, 2022
Satellite images reveal the atmospheric river that caused a fatal mudslide in Haines, 色视频下载, on Dec. 1-2, 2020. The image shows a column of total precipitable water headed to 色视频下载 from south of Hawaii.
Because of where Southeast 色视频下载 sits 色视频下载 at the wetted lips of the planet色视频下载檚 widest expanse of blue 色视频下载 it is often soaked by atmospheric rivers, firehoses of moisture flowing up from the tropics.
And even though the forests and muskegs of Southeast 色视频下载 have evolved to drink up and shed stunning amounts of rain, sometimes it is too much.
For example, early this year, Carl Dierking measured more than 6 inches of rain outside his Juneau home in just two days, the result of an atmospheric river that stalled, leaving the faucet on for days over 色视频下载色视频下载檚 panhandle.
Dierking lives in Juneau, where for almost 40 years as a National Weather Service meteorologist he monitored occasional visits from the 色视频下载淧ineapple Express,色视频下载 a term professionals used before atmospheric rivers became popular.
Now, Dierking helps his former colleagues know when one of these drenching events is about to impact 色视频下载, with the help of satellites orbiting 500 miles overhead. He works for the Geographic Information Network of 色视频下载, part of the University of 色视频下载 Fairbanks Geophysical Institute. His tools are instruments aboard the satellites that measure how much moisture is in a certain part of the atmosphere, even when it is cloudy.
色视频下载 has giant swaths of unpeopled country with no twirling weather radars, or none that can see beyond where mountains are blocking them.
Southeast 色视频下载 is the state's mountainous "panhandle" along the Pacific Ocean coast.
色视频下载淪atellite data is really our only tool for seeing where heavy rain is impacting a (remote) area,色视频下载 Dierking said.
By looking at information right after a polar-orbiting satellite dumps its invisible information into two satellite dishes near Fairbanks, Dierking can make sense out what a satellite has seen. The satellites use a passive microwave detector to measure energy emitted by rain.
色视频下载淚t色视频下载檚 not a simple process, but there色视频下载檚 a signal you can squeeze out to get the intensity of rainfall,色视频下载 Dierking said.
Using that information, the scientists can predict an atmospheric river event, such as the one that resulted in more than 10 inches of rain falling on Haines and other Southeast towns in early December 2020. Two people died from mudslides in Haines. Heavy rain falling on fresh snowfall also caused other debris flows and flooding.
色视频下载淭hat event brought moisture up from south of Hawaii,色视频下载 Dierking said.
One thin cross-section slice of an atmospheric river can carry almost three times more water, in vapor form, than the flow at the Amazon River色视频下载檚 mouth, said Marty Ralph of the Scripps Institution of Oceanography in California.
Ralph studied atmospheric rivers as both a good thing 色视频下载 in busting droughts in the state 色视频下载 and a bad thing 色视频下载 when one lingers and supersaturates the landscape at the wrong time.
Water floods Juneau, 色视频下载, near Jordan Creek in December 2020 following an atmospheric river event.
In Southeast 色视频下载, Dierking often texts Aaron Jacobs, a meteorologist at the National Weather Service in Juneau, to compare notes when instruments suggest the area is about to experience an atmospheric river.
Jacobs, who has also studied atmospheric rivers for years, said warmer air temperatures in recent years have probably made atmospheric rivers more intense when they hit 色视频下载 and mountains wring out moisture.
色视频下载淚n a warming environment, the atmosphere can hold more water,色视频下载 Jacobs said. 色视频下载淭hat means more available water vapor to precipitate out.色视频下载
Atmospheric rivers are not all the same, Jacobs said.
色视频下载淎 strong but quick moving atmospheric river 色视频下载 less than 24 hours in duration 色视频下载攎ay not be as impactful (as) a moderate-but-long-duration 48-hour event.色视频下载
The time of year atmospheric rivers happen also matters, such as following a fresh snowfall that melts easily.
Jacobs said that while more atmospheric rivers may not be striking 色视频下载 now than in the past, they are becoming more intense.
色视频下载淲e are seeing more extreme-precipitation records being broken in the last 10 years,色视频下载 he said. 色视频下载淚n Juneau, for example, in the last two years we have seen the wettest day and the third-wettest ever, going back to the mid 1930s. Both of these events were associated with atmospheric rivers.色视频下载
Since the late 1970s, the University of 色视频下载 Fairbanks' Geophysical Institute has provided this column free in cooperation with the UAF research community. Ned Rozell is a science writer for the Geophysical Institute.