Netherlands – The eclipse affects many things on Earth, including the behavior of animals and radio waves in the atmosphere, and also causes low clouds to dissipate.
As the eclipse begins, the clouds quickly clear. Scientists found that cumulonimbus cloud cover (which are very dense and massive clouds) decreased as the moon’s shadow passed over the Earth during the annular eclipse in 2005.
Scientists have suggested that this little-studied aspect of a solar eclipse contains important lessons for geoengineering efforts aimed at blocking sunlight.
Solar eclipses occur anywhere from two to five times a year, and these events provide great opportunities for scientific investigations, said Victor J. H. Trees, a geologist at Delft University of Technology in the Netherlands. He added that solar eclipses are unique experiments that allow researchers to study what happens when sunlight is quickly blocked. “It’s completely different from the normal day-night cycle.”
Trez and his colleagues recently analyzed cloud cover data obtained during the 2005 annular eclipse, which was visible in parts of Europe and Africa. They extracted visible and infrared images collected by two geostationary satellites operated by the European Organization for the Exploitation of Meteorological Satellites.
The team focused on a square area extending 5 degrees in both latitude and longitude and centered over South Sudan, and tracked the evolution of the cloud for several hours before the eclipse, during the eclipse, and for several hours afterward.
Low-level cumulonimbus clouds were strongly affected by the degree of blocking of the sun. The cloud cover began to decrease when it covered about 15% of the face of the sun, that is, about 30 minutes after the beginning of the eclipse. The clouds began to return about 50 minutes after maximum darkness.
While typical cloud cover hovered around 40% in non-eclipse conditions, less than 10% of the sky was covered in clouds during the period of maximum dimming, the team noted.
“On a large scale, the cumulus clouds are starting to disappear,” Trees said.
Trees explained that the Earth’s temperature is important when it comes to cumulus clouds, because it is low enough to be greatly affected by everything that happens on the Earth’s surface.
It is not surprising that Earth’s surface temperatures decrease as the Moon increasingly blocks sunlight.
“We knew that even small changes in solar radiation have an impact on Earth’s surface temperature,” said Virendra Ghat, an atmospheric scientist at Argonne National Laboratory in Lemont, Illinois, who was not involved in the research.
Scientists estimated that the maximum change in Earth’s surface temperature was about 6 degrees Celsius during the 2005 eclipse. They also found that the surface temperature decreased in conjunction with the blocking portion, without any significant time delay. This is consistent with observations made during other solar eclipses.
The scientists concluded that the apparent drop in Earth’s surface temperature during a solar eclipse is what drives changes in cumulonimbus cloud cover.
This makes sense, Gatt said, because cumulonimbus clouds form when warm, relatively humid air rises from the Earth’s surface, cools, and eventually condenses into cloud droplets. She continued that when Earth’s surface temperatures decrease, there is a smaller temperature gradient near the Earth’s surface, and therefore a smaller force that pushes the air forming the clouds upward.
The delays that Trees and his colleagues observed between the beginning of the eclipse and when the clouds began to dissipate, and also between the time of maximum dimming and when the clouds began to return, reveal what is called the boundary layer, which is the lowest level of the Earth’s atmosphere. Each of these lags has a physical meaning, Trees said: “It tells us how fast the air is rising.”
Source: Space
#clouds #dissipate #solar #eclipse
2024-04-08 01:08:21