How to Kill Zombie Hurricanes
Jason Ahrns, a graduate student at the University of Alaska-Fairbanks, goes sprite-chasing at night during electrical storms. Here he captures column-shaped red sprites over Red Willow County, Nebraska, on Aug. 12, 2013.
A “jellyfish” sprite photographed over Republic County, Kansas, on August 3, 2013. "I have very good low light eyesight, and I've watched tons of sprites in real time on the context cameras so I know exactly what and where to look. I was watching intently out the window while I snapped these shots, and the camera caught a sprite that I didn't see," writes Ahrns in his blog: http://musubk.blogspot.fr/2013/08/sprites-2013-update-4.html
Like flames from a butane lighter, three blue jets (slightly blurred due to the motion of the aircraft) appear above the lightning-lit clouds in this photo taken over Republic County, Kansas, on August 3, 2013. Ahrns describes this picture as the "the cream of the crop," due to the difficult nature of capturing blue jets. "Since jets tend to hug the top of the clouds it's understandable that they're more difficult for a ground observer to see/photograph, so it makes sense that being up in a sprite-chasing aircraft would give me a serious advantage," he writes.
"Unlike sprites, blue jets aren’t directly triggered by lightning, but seem to be somehow related to the presence of hail storms," reports the Smithsonian: http://blogs.smithsonianmag.com/artscience/2013/08/scientists-capture-rare-photographs-of-red-lightning/.
Red sprite over Canadian County, Oklahoma, on August 6, 2013. "I was also able to see quite a few jets with my naked eyes! That's a first for me, and I'm always excited to see a new sky phenomenon for myself. I still haven't been able to see a sprite naked-eye, and it impresses me just how difficult that actually is," Ahrns writes.
Ahrns' Nikon D7000 on a flexible tripod points out the window of the sprite-chasing aircraft, a Gulfstream V with the National Center for Atmospheric Research. "I butted the camera up against the window glass and put my weight on it to get rid of most of the wobbles and light leaks, but the motion of the aircraft itself still showed up, especially when we hit a patch of turbulence (we are, you know, flying right next to a thunderstorm)," he writes.
Twice now in recent weeks a hurricane has died and then come back to life. It’s unfair, but not particularly unnatural.
To understand these Franken-storms, however, it’s helpful to forget about hurricanes for a minute and consider the conditions that create them: Intense low pressure areas over warm ocean waters, which supply the storm energy, and lower the pressure more, by way of warm water vapor evaporating and rising from the sea surface.
You also need winds to be pretty much aligned at low and high elevation so that wind shear doesn’t lop off the tops of thunderheads. If all this is in place, the intensifying low pressure area causes air to spiral in towards the center, which makes it windy and can intensify the evaporation even more.
There’s a lot more to it, but these are the basic ingredients.
Tropical Storm Humberto, which was briefly the first hurricane of the season last week, died on Sept. 15 when its high cloud tops were ripped off by wind shear. That reduced the storm to little more than a low pressure area. But a day later the wind shear had abated and all the other conditions — warm ocean waters and low pressure — were still ripe for a storm, and so Humberto sprang back life and is now continuing west across the Atlantic towards the United States.
The zombie sibling of Humberto is Gabrielle from earlier this month. Gabrielle was a Tropical Storm in the eastern Atlantic until she too was ripped apart, only to be resurrected into a tropical storm, which headed northwest, She eventually died in the northern Atlantic without hitting land.
This time she’ll not be reviving, since she has no more warm waters to keep her alive.
Photo: Will they live? On Sept. 15, Manuel, left, was a tropical storm with winds of 55 knots (102 km/hr or 63 miles per hour). Ingrid, right, was a Category 1 hurricane with winds of 65 knots (120 km/hr or 75 mi/hr). NASA image courtesy Jeff Schmaltz, LANCE/EOSDIS MODIS Rapid Response Team at NASA GSFC.