Research Roundup: Plane-Punched Clouds, the Sahel and More

Plane-Punched Clouds
Here’s a bit of news that ufologists may not like to hear. A new study offers more evidence that airplanes produce the saucer-shaped cloud formations that atmospheric scientists call “hole-punch clouds.” The researchers — including Langley-based Patrick Minnis — found that planes seed the unusual clouds by supercooling air in the wake of propellers and wing tips. The chilled air generates tiny ice droplets that can lead to snow or rainfall. If the precipitation falls quickly enough and the cloud is thin, hole-punch clouds can form. Cloud-punching planes don’t produce enough extra precipitation to impact the global climate, the lead author of the study said, but the effect is widespread. The same process, the Earth Observatory pointed out in 2009, can create narrow “canal clouds” as well.

The Slippery Sahel
The Sahel, an area of semi-arid grassland around the southern limit of the Sahara Desert, is thought to be one of the areas most vulnerable to climate change. Most people in the region rely on rain-fed agriculture, and devastating famines that killed as many as 100,000 people struck the area in the 1970s. But how well can climatologists predict how Sahel precipitation patterns will change over the next 100 years? As part of a new review paper, GISS scientist Leonard Druyan surveyed the literature and found projections are all over the map. Here’s how he explained it: “A variety of model deficiencies, regarding the simulation of one or more of these physical processes, taints models’ climate change projections. Consequently, no consensus emerges regarding the impact of anticipated greenhouse gas forcing on the hydrology of the Sahel in the second half of the 21st century.”

Soil Matters
Soil moisture. Sounds boring, I know. But did you know that patches of dry soil, in certain situations, can actually spark precipitation in ways thatmoist areas don’t? That’s the takeaway of a Nature Geoscience piece penned by Goddard’s Randal Koster that offers a perspective on researchthat suggests storms paradoxically form more easily over areas thathave sharp gradients between moist and dry soil. More work needs to bedone to confirm the finding, but in the meantime here’s to hoping thismeans the less I water my tomatoes the more it will rain.

Get Ready for GPM
You might think the work starts for scientists after a satellite reaches orbits and starts beaming data back to Earth. In fact, studies on the ground and in the lab actually start years – in some cases decades – in advance of a satellite getting anywhere near a rocket. Take, for example, NASA’s Global Precipitation Mission (GPM). Two studies appeared recently that, while not exactly Earth-shattering, lay the scientific groundwork for juicer findings that will come when the core GPM spacecraft launches in July of 2013. One involves a suite of modeling tests that will help researchers do a better job of integrating satellite rainfall data into models. The other proposes a new mathematical approach that will make measurements of rainfall made by microwave instruments over land more accurate.

Polar Bears, Martha Stewart, and Me
You just can’t go wrong with a title to a talk like that. The clip below is from an hour-long talk that Gavin Schmidt gave to colleagues at GISS about his visit to Churchill, a tiny town in Canada that’s known as the polar bear capitol of the world. Yes, Martha Stewart came along as well. The talk doesn’t start until about 1:48, and Schmidt’s interview with Stewart starts at 48:18.

Text by Adam Voiland. Hole-punch cloud photo was published originally on Earth Science Picture of the Day. The photographer is Herbert Raab.