Atmospheric rivers are meteorological phenomenon that we humans only discovered in 1998 and which supply about 30-to-50 percent of California's annual precipitation. In the NOAA satellite image above, the atmospheric river is visible as a thin yellow arm, reaching out from the Pacific to touch California. Or, more evocatively, reaching out to slap California silly with a gushing downpour.
An atmospheric river is a narrow conveyor belt of vapor about a mile high that extends thousands of miles from out at sea and can carry as much water as 15 Mississippi Rivers. It strikes as a series of storms that arrive for days or weeks on end. Each storm can dump inches of rain or feet of snow.
The real scare, however, is that truly massive atmospheric rivers that cause catastrophic flooding seem to hit the state about once every 200 years, according to evidence recently pieced together (and described in the article noted above). The last megaflood was in 1861; rains arrived for 43 days, obliterating Sacramento and bankrupting the state.
As you might guess, climate change is also involved. Evidence suggests that warming global temperatures could increase the frequency of atmospheric rivers. That, combined with the 200-year event expected soon and the fact we're learning so much much more about these storms, means that you should expect to hear the phrase "atmospheric river" more often.
Scientific American has two interesting stories on the phenomenon right now. The first, which I quote from above, is a blog post by Mark Fischetti. The second is a much longer feature story that gets into the forces that cause these storms and the climate change connection.
The more accurate version of this question would really be something like, "Why do some trees fall over in a storm while others stay standing?" The answer is more complex than a simple distinction between old, rotted, and weak vs. young, healthy, and strong. Instead, writes Mary Knudson at Scientific American blogs, trees fall because of their size, their species, and even the history of the human communities around them.
“Trees most at risk are those whose environment has recently changed (say in the last 5 – 10 years),” Smith says. When trees that were living in the midst of a forest lose the protection of a rim of trees and become stand-alones in new housing lots or become the edge trees of the forest, they are made more vulnerable to strong weather elements such as wind.
They also lose the physical protection of surrounding trees that had kept them from bending very far and breaking. Land clearing may wound a tree’s trunk or roots, “providing an opportunity for infection by wood decay fungi. Decay usually proceeds slowly, but can be significant 5-10 years after basal or root injury.” What humans do to the ground around trees — compacting soil, changing gradation and drainage “can kill roots and increase infection,” Smith warns.
Read the full piece at Scientific American Blogs
Image: West Philly Storm - Trees Down, a Creative Commons Attribution (2.0) image from kwbridge's photostream
The images above — prepared by NASA hurricane researcher Owen Kelly — were taken on Sunday, before Hurricane Sandy made landfall on the United States' Northeast coast. They're made from radar data collected by the Tropical Rainfall Measuring Mission (TRMM) satellite, and they show a feature of this storm that helps explain why it's caused much more destruction than you might expect from a Category 1 hurricane.
In the right-hand image, showing a close-up of the storm's eye, you can see a feature labeled "eyewall". Those are vertical cloud walls that surround the eye, and they're the spot with the strongest winds in the whole storm.
Placed in context, the TRMM-observed properties of Hurricane Sandy’s eyewall are evidence of remarkable vigor. Most hurricanes only have well-formed and compact eyewalls at category 3 strength or higher. Sandy was not only barely a category 1 hurricane, but Sandy was also experiencing strong wind shear, Sandy was going over ocean typically too cold to form hurricanes, and Sandy had been limping along as a marginal hurricane for several days.
That eyewall, says NASA and New Scientist, is the result of Sandy's Frankenstorm nature. Despite all the factors that should have made this storm weak, it represented the merging of several storm systems. Because of that, Sandy was stronger than a Category 1 storm normally is.
Read the full story on this at NASA and New Scientist
Via Michael Marshall
Tornado-loving BB pal Jody Radzik just turned me on to Extreme Instability, a collection of one intrepid storm chaser's breathtaking weather photography. The above photo that I've taken it upon myself to title "Act of God" is from a bow echo in Watertown, South Dakota on August 3. The photographer: "I'm driving along, having gained at least a small bit of ground again, when I see this white cross and a roadside chapel next to the road. No way. Slam on the brakes, pull over and jump out of the car and shoot fast fast." Extreme Instability
During the storm a couple of nights ago, we heard an almighty thunderclap and our dogs came dashing into the house. Once the rain ebbed and we went outside, we found this scene just around the corner: a wall apparently blown to pieces, with cinderblock chunks thrown as far as 40 or 50 feet. It seems too far for a plain old wall collapse. Could that have been caused by the lightning strike? If so, how? Steam pressure from the waterlogged bricks being suddenly superheated, like a tree strike?
Read the rest