by The splendor of a solar eclipse is unique to our world – nowhere else in the solar system does a planet’s moon block sunlight so perfectly. The rapid darkening of these events affects many things on Earth, including the behavior of animals and waves in the ionosphere.
Researchers have now found that cumulus cloud cover dropped by more than a factor of 4, on average, as the moon’s shadow passed over Earth during a recent annular eclipse.
This small study of solar eclipses has important lessons for geoengineering efforts aimed at blocking sunlight, the team suggested.
Related: What if it is cloudy for the solar eclipse April 8?
Experiments in the sky
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Solar eclipses occur anywhere from 2 to 5 times a year, and these events provide neat opportunities for scientific investigations, said Victor JH Trees, a geoscientist at Delft University of Technology in the Netherlands. msgstr “Solar eclipses are unique experiments.” They allow researchers to study what happens when sunlight is quickly obscured, he said. “They are very different than the normal day-night cycle.”
Trees and his colleagues recently analyzed cloud cover data obtained during an annular eclipse in 2005, visible in parts of Europe and Africa. They analyzed visible and infrared images collected by two geostationary satellites operated by the European Organization for the Exploitation of Meteorological Satellites. Getting to space was critical, Trees said. “If you really want to quantify how clouds behave and how they react to a solar eclipse, it helps to study a large area. That’s why we want to look from space.”
The researchers focused on a square region spanning 5° in both latitude and longitude centered on South Sudan. With a bird’s eye view, they tracked the evolution of the clouds for several hours before the eclipse, during the eclipse, and for several hours after.
Farewell, sun; Farewell, clouds
Low-level clouds – which tend to peak at a height of around 2 kilometers (1.2 miles) – were greatly affected by the amount of solar obscuration. Cloud cover began to decrease when about 15% of the face of the sun was covered, about 30 minutes after the start of the eclipse. The clouds only started to return about 50 minutes after maximum obscurity. And while typical underground cloud cover was about 40% in oneclipse conditions, less than 10% of the sky was covered by clouds during maximum obscurity, the team noted.
“On a large scale, the cumulus clouds began to disappear,” said Trees.
To dig into the physics behind their observations, Trees and his colleagues collected land surface temperature measurements from the same two geostationary satellites. Ground temperatures are important for cumulus clouds, Trees said, because they are low enough to have a significant impact on whatever happens at the Earth’s surface.
Not surprisingly, the earth’s surface temperatures dropped as the moon blocked more sunlight. “We knew that even small changes in solar radiation affect the surface temperature of the earth,” said Virendra Ghate, an atmospheric scientist at Argonne National Laboratory in Lemont, Ill., who was not involved in the research.
The researchers estimated that there would be a maximum change of nearly 6°C in the earth’s surface temperature for the 2005 eclipse. They also found that the surface temperature in the green phase decreased with the obscuration fraction, without any significant time delay. That is consistent with observations made during other solar eclipses.
Follow the heat
The significant decrease in the surface temperature of the earth during a solar eclipse is what is driving the changes in the cover of the cumulus cloud, according to researchers. That’s logical, Ghate said, because cumulus clouds form when relatively warm and moist air rises from the Earth’s surface, cools, and eventually condenses into cloud droplets. When the land surface temperature drops, there is less of a temperature gradient near the Earth’s surface and so there is less force driving air that forms a cloud upwards, he said. “You do not have the source of prosperity.”
The delays observed by Trees and his colleagues – between the start of the eclipse and when the clouds began to disperse and also between the time of maximum obscuration and when the clouds began to return – reveal something about the so-called boundary layer, the lowest level of Earth’s land. atmosphere. Each of those lags has a physical meaning, Trees said. “It tells us how fast the air is rising.”
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Besides shedding light on the physics of cloud dissipation during solar eclipses, these new findings also have implications for future geoengineering efforts, Trees and his colleagues suggested. Discussions are underway to mitigate the effects of climate change, for example, by seeding the atmosphere with aerosols or by sending solar reflectors into space to prevent some of the sunlight from reaching Earth. Such geoengineering holds the promise of cooling our planet, the researchers agree, but its consequences are largely unexplored and could be widespread and irreversible.
These new findings suggest that geoengineering efforts involving solar obscuration may reduce cloud cover. And because clouds reflect sunlight, the effectiveness of any effort could decrease accordingly, Trees said. That’s an effect that needs to be taken into account when considering different options, the researchers said.
This article was originally published Eos.org.
