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posted by janrinok on Tuesday September 14, @05:11AM   Printer-friendly [Skip to comment(s)]
from the space-for-improvement dept.

Stanford scientists solve mystery of icy plumes that may foretell deadly supercell storms:

Stanford scientists solve mystery of icy plumes that may foretell deadly supercell storms

The most devastating tornadoes are often preceded by a cloudy plume of ice and water vapor billowing above a severe thunderstorm. New research reveals the mechanism for these plumes could be tied to "hydraulic jumps" – a phenomenon Leonardo Da Vinci observed more than 500 years ago.

When a cloudy plume of ice and water vapor billows up above the top of a severe thunderstorm, there's a good chance a violent tornado, high winds or hailstones bigger than golf balls will soon pelt the Earth below.

A new Stanford University-led study, published Sept. 10 in Science, reveals the physical mechanism for these plumes, which form above most of the world's most damaging tornadoes.

[...] Understanding how and why plumes take shape above powerful thunderstorms could help forecasters recognize similar impending dangers and issue more accurate warnings without relying on Doppler radar systems, which can be knocked out by wind and hail – and have blind spots even on good days. In many parts of the world, Doppler radar coverage is nonexistent.

"If there's going to be a terrible hurricane, we can see it from space. We can't see tornadoes because they're hidden below thunderstorm tops. We need to understand the tops better," said O'Neill, who is an assistant professor of Earth system science at Stanford's School of Earth, Energy & Environmental Sciences (Stanford Earth).

Journal Reference:
1.) Morgan E O’Neill, Leigh Orf, Gerald M. Heymsfield, et al. Hydraulic jump dynamics above supercell thunderstorms, Science (DOI: 10.1126/science.abh3857)
2.) Ivan Marusic, Susan Broomhall. Leonardo da Vinci and Fluid Mechanics [open], Annual Review of Fluid Mechanics (DOI: 10.1146/annurev-fluid-022620-122816)

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  • (Score: 2) by krishnoid on Wednesday September 15, @12:54AM

    by krishnoid (1156) on Wednesday September 15, @12:54AM (#1177911)

    From an engineering perspective, how would building codes be changed to withstand such storms? Let's assume storms show up in this intensity, say once every couple weeks during a bad season.

  • (Score: 0) by Anonymous Coward on Wednesday September 15, @02:18AM

    by Anonymous Coward on Wednesday September 15, @02:18AM (#1177946)

    I don't think this article does a good job of explaining what's actually happening here.

    Part of this is probably about understanding how water vapor enters the stratosphere.. Water vapor is a very potent greenhouse gas. Water vapor should have a long residence time in the stratosphere as opposed to the troposphere. It stands to reason that water vapor in the stratosphere might have a greater effect than in the troposphere simply because water vapor in the stratosphere stays in the atmosphere longer. It's definitely worthwhile understanding the water vapor budget in the stratosphere, how water vapor enters, and how it leaves the stratosphere. Understanding the dynamics involved at the scale of individual thunderstorms is useful and might allow models to better simulate these processes.

    Although the Science article is behind a paywall, I think the mechanism seems reasonable. The basic dynamics that were described, such as the overshooting top acting as an obstacle to upper level flow, are reasonable though somewhat simplistic. Weaker momentum from the lower atmosphere is brought upward in the thunderstorm updraft, which overshoots its equilibrium level, creating the overshooting top. As stronger upper level winds converge with the weaker winds from below, this creates a pressure perturbation that deflects the upper level winds around the updraft. We see evidence for this in the radar appearance of some supercell thunderstorms, where the stronger reflectivity splits around the updraft, creating a flying eagle appearance. The idea of a hydraulic jump downstream seems reasonable, too. The idea that upper level flow forced around the overshooting top and accelerate while doing so is reasonable, as is that a hydraulic jump might occur downstream when the winds slow. It's reasonable that this could loft ice crystals into the stratosphere. No argument here, the mechanism seems legitimate to me.

    It seems likely that the phenomenon described here is linked to processes in the thunderstorm updraft that may increase the probability of high-end severe weather like tornadoes. That seems plausible, and there are studies that use polarimeteric radar signatures to try to identify precursors to tornadogenesis. As with this work, the goal is to identify signatures that may allow for tornado warnings to be issued with longer lead times.

    There is some good research about what happens in the upper atmosphere in supercell thunderstorms. Here's a preprint that addresses why the idea of obstacle flow is wrong: []. And here's a poster describing this particular study: []. And here's the paper linking this signature to severe weather, particularly hail: [].

    The key point is that thunderstorms that exhibit this signature tend to be much more prolific at generating high-end severe weather than those that do not, and that this may provide more lead time to forecasters to issue warnings. It's not that the above-anvil cirrus plume causes severe weather, but rather that it is an indicator of processes occurring in the updraft that are also linked to severe weather, especially hail.