At first glance, a weather forecaster for Venus would have either a really easy or a really boring job, depending on your point of view. The climate on Venus is widely known to be unpleasant —at the surface, the planet roasts at more than 800° Fahrenheit (425° Celsius) under a suffocating blanket of sulfuric acid clouds and a crushing atmosphere more than 90 times the pressure of Earth's. Intrepid future explorers should abandon any hope for better days, however, because it won't change much.
"Any variability in the weather on Venus is noteworthy because the planet has so many features to keep atmospheric conditions the same," said Tim Livengood, a researcher with the National Center for Earth and Space Science Education, Capitol Heights, Maryland, and now with the University of Maryland, College Park.
"Earth has seasons because its rotation axis is tilted by about 23°, which changes the intensity of sunlight and the length of the day in each hemisphere throughout the year,” explained Livengood, who is stationed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “However, Venus has been tilted so much, it's almost completely upside down, leaving it with a net tilt of less than 3° from the Sun, so the seasonal effect is negligible. Also, its orbit is even more circular than Earth's, which prevents it from getting significantly hotter or cooler by moving closer to or farther away from the Sun. And while you might expect things to cool down at night — especially since Venus rotates so slowly that its night lasts almost 2 Earth months — the thick atmosphere and sulfuric acid clouds act like a blanket while winds move heat around, keeping temperatures pretty even. Finally, almost all the planet's water has escaped to space, so you don't get any storms or precipitation like on Earth where water evaporates and condenses as clouds."
However, higher up, the weather gets more interesting, according to a new study of old data by NASA and international scientists. The team detected strange things going on in data from telescopic observations of Venus in infrared light at about 68 miles (110 kilometers) above the planet's surface, in cold, clear air above the acid clouds, in two layers called the mesosphere and the thermosphere.
"Although the air over the polar regions in these upper atmospheric layers on Venus was colder than the air over the equator in most measurements, occasionally it appeared to be warmer," said Theodor Kostiuk of Goddard. "In Earth's atmosphere, a circulation pattern called a 'Hadley cell' occurs when warm air rises over the equator and flows toward the poles, where it cools and sinks. Since the atmosphere is denser closer to the surface, the descending air gets compressed and warms the upper atmosphere over Earth's poles. We saw the opposite on Venus. In addition, although the surface temperature is fairly even, we've seen substantial changes — up to 54° Fahrenheit (about 30 kelvin change) — within a few Earth days in the mesosphere — thermosphere layers over low latitudes on Venus. The poles appeared to be more stable, but we still saw changes up to 27° Fahrenheit (about 15 K change)."
"The mesosphere and thermosphere of Venus are dynamically active," said Guido Sonnabend of the University of Cologne, Germany. "Wind patterns resulting from solar heating and east to west zonal winds compete, possibly resulting in altered local temperatures and their variability over time."