December 10, 2013
Long-Standing Mystery Of Tropospheric Warming Finally Solved
Lee Rannals for redOrbit.com - Your Universe Online
A long-standing mystery surrounding unusual warming of planetary atmospheres is not just exclusive to our solar system, but is most likely universal, according to a paper published in the journal Nature Geoscience.
In 1902 a scientist named Léon Teisserenc de Bort found a point in Earth’s atmosphere where the air stops cooling and begins growing warmer. This finding was surprising considering scientists knew that as you climb in altitude, the air grows colder and thinner.
De Bort named this mysterious region in the atmosphere the 'tropopause' because it sits between the stratosphere and the troposphere. In the 1980s a NASA spacecraft found that Earth isn’t the only planet in our solar system with tropopauses. The space agency discovered that Jupiter, Saturn, Uranus and Neptune all have tropopauses, as well as Saturn’s largest moon Titan. NASA also found that the tropopause point on these planets occur at roughly the same level in the atmosphere.
The explanation as to why these planets, and moon, all have tropopauses occurring at a pressure of around 0.1 bar in the atmosphere has been a bit of a mystery to scientists. All of the objects have great differences in atmospheric composition, gravity, internal heat and sunlight. However, in all of these bodies, the tropopause separates a stratosphere with a temperature profile that is controlled by the absorption of short-wave solar radiation.
The new study suggests that tropopauses are probably common to billions of thick-atmosphere planets and moons throughout the Milky Way.
Researchers say that the explanation lies in the physics of infrared radiation. Atmospheric gases gain energy by absorbing infrared light from the surface of a rocky planet or from the deeper parts of the atmosphere of a planet like Jupiter, which has no surface.
The team used an analytic model to show that at high altitudes atmospheres become transparent to thermal radiation due to the lower pressure. Above the level where the pressure is, the absorption of visible, or ultraviolet, light causes the atmospheres of the planets to grow warmer as altitude increases.
The scientists say the physics should apply to the vast number of planetary atmospheres with stratospheric gases that absorb ultraviolet or visible light. Astronomers could use this rule of thumb to extrapolate temperature and pressure conditions on the surface of planets and work out whether the worlds are potentially habitable.
“We know that temperatures are going to increase below the tropopause, and we have some models for how we think those temperatures increase — so given that leg up, we can start to extrapolate downward toward the surface,” said astronomer Tyler Robinson of the University of Washington. “It’s neat that common physics not only explains what’s going on in solar system atmospheres, but also might help with the search for life elsewhere.”