Tornadoes are frequently preceded by a hazy plume of ice and water vapor billowing above a strong thunderstorm. According to new research, the mechanism for these plumes could be linked to ‘hydraulic jumps,’ a phenomena identified by Leonardo Da Vinci more than 500 years ago.
When a foggy plume of ice and water vapor billows up over the top of a severe thunderstorm, there’s a good possibility a tornado, powerful winds, or hailstones the size of golf balls may soon pound the Earth below.
A new study lead by Stanford University and published in Science uncovers the physical process for these plumes, which build above the majority of the world’s most destructive tornadoes. Previous study has shown that they are easy to detect in satellite photography, frequently 30 minutes or more before severe weather arrives on the ground. “Why is this plume related with the worst conditions, and how does it exist in the first place? That is the void we are attempting to fill “Morgan O’Neill, primary author of the current study, is an atmospheric scientist.
The findings come little over a week after supercell thunderstorms and tornadoes spun up within the remains of Hurricane Ida as it slammed into the United States’ Northeast, compounding the destruction caused by record-breaking rains and flash floods.
We can see if there will be a major hurricane from space. Tornadoes are invisible because they are shrouded behind thunderstorm tops. We need to learn more about the tops.Morgan O’Neill
Understanding how and why plumes form above powerful thunderstorms could assist forecasters in recognizing comparable imminent threats and issuing more precise warnings without depending on Doppler radar systems, which can be knocked out by wind and hail and have blind spots even on favorable days. Doppler radar coverage is non-existent in many parts of the planet.
“We can see if there will be a major hurricane from space. Tornadoes are invisible because they are shrouded behind thunderstorm tops. We need to learn more about the tops” O’Neill, an assistant professor of Earth system science at Stanford’s School of Earth, Energy, and Environmental Sciences, made the statement (Stanford Earth).
Supercell storms and exploding turbulence
Most tornadoes are spawned by supercell thunderstorms, a unique form of storm with a whirling updraft that may hurtle aloft at speeds of more than 150 miles per hour, with enough force to punch through the typical lid on Earth’s troposphere, the lowest layer of our atmosphere.
Rising currents of moist air tend to flatten and spread out when they reach this cap, known as the tropopause, generating an anvil-shaped cloud in lesser thunderstorms. The powerful updraft of a supercell thunderstorm pushes the tropopause upward into the next layer of the atmosphere, resulting in what scientists call an overshooting top. “It’s like a fountain pressing up against our next layer of atmosphere,” O’Neill explained.
As winds in the high atmosphere run over and around the protruding storm top, they occasionally whip up streams of water vapor and ice that shoot into the stratosphere to produce the recognizable plume, known technically as an Above-Anvil Cirrus Plume, or AACP.
The rising air of the overshooting top quickly returns to the troposphere, like a ball accelerating downhill after cresting high. At the same time, air is racing down the shielded side of the dome from the stratosphere.
O’Neill and colleagues discovered this ignites a downslope windstorm in the tropopause, where wind speeds surpass 240 miles per hour, using computer simulations of idealized supercell thunderstorms. “This incredibly narrow, insanely rapid jet is formed by dry air descending from the stratosphere and wet air ascending from the troposphere. In turbulence, the jet becomes unstable, and the entire thing mixes and explodes “According to O’Neill. “These storm top speeds have never been observed or hypothesized before.”
Overshooting storm tops of moist air rising into the upper atmosphere have long been recognized by scientists as physical impediments that can obstruct or alter airflow. It’s also been suggested that waves of wet air flowing over these peaks can break and loft water into the stratosphere. However, no research has been conducted to date to explain how all of the pieces come together.
According to the new modeling, the explosion of turbulence in the atmosphere that occurs with plumed storms is caused by a phenomena known as a hydraulic jump. The same mechanism is at work when rushing winds blow over mountains, causing turbulence on the downslope side, or when water hurtling down a dam’s spillway abruptly bursts into froth when it meets slower-moving water below.
As early as the 1500s, Leonardo DaVinci observed the phenomena in flowing water, and ancient Romans may have attempted to prevent hydraulic jumps in aqueduct designs. However, atmospheric scientists have only seen the dynamic caused by solid topography up to this point. According to the new modeling, a hydraulic jump can also be induced by fluid impediments in the atmosphere that are almost totally formed of air and change shape every second, kilometers above the Earth’s surface.
According to the calculations, the start of the jump coincides with a fairly rapid injection of water vapor into the stratosphere, at rates of up to 7000 kilos per second. This is two to four times more than earlier projections. Water may remain in the stratosphere for days or weeks after reaching it, potentially impacting the amount and quality of sunlight that reaches Earth by destroying ozone in the stratosphere and warming the planet’s surface. “In our plume simulations, water reaches deep into the stratosphere, where it may have a longer-term climatic influence,” said co-author Leigh Orf, an atmospheric scientist at the University of Wisconsin-Madison.
According to O’Neill, NASA research planes at high altitudes have only lately developed the ability to study three-dimensional winds at the tops of thunderstorms, and have yet to detect AACP generation at close range. “We now have the technology to go validate our modeling results to determine if they’re realistic,” said O’Neill. “In science, that’s a very sweet spot.”