Why do some clouds disappear during a solar eclipse?

There have been eight eclipses worldwide since 1990 but the last total solar eclipse occurred on 11 August 1999. For those who remember, it was a strange experience - clear blue skies darkened, ebbing into a dull color followed by an eerie silence - wildlife and in particular birds, who provide a constant audible backdrop to our lives, seemed to vanish out of sight, neither seen nor heard. Where did they go? What was it about the eclipse that disturbed them? One theory is that animals perceive the drop in light and temperature to signal that night is about to fall.

Clouds vanish then reappear

Another common phenomenon during a total solar eclipse is cloud dissipation. In layman’s terms, that means that clouds, usually low-level cumulus clouds more than other classes, will evaporate, disappearing from view.

Clouds are composed of liquid-suspended water droplets in an environment close to 100% relative humidity. They form when thermals - bubbles of buoyant air, rise, then cool, condensing into clouds. The condensation level is typically around 600 meters in winter and twice that in the summer months and is entirely dependent on the atmospheric conditions of the day - and more importantly, the temperature.

Temperature drop, feels like dusk

During a total solar eclipse, average temperatures drop about 5 degrees Celsius (10 degrees Fahrenheit) - occasionally more, depending on location and the time of year. The temperature drop occurs when the moon temporarily blocks out the sun’s rays. Most of the sun’s energy warms the ground, which in turn, gradually warms the air; the warm air rises, and cool air settles on the ground, creating a convection cycle of heating. This delayed transfer of heat could explain the slight delay in the cooling of the air during totality.

During totality there is also a chance of a full, 360-degree sunset, in every direction on the horizon. Once the eclipse is over, the sun reemerges and temperatures return to where they were before, clouds will start to reappear. From First to Fourth Contact takes about two and a half hours. Animals return, thinking that the morning has arrived and birdsong can be heard once again.

On April 8, 2024, parts of North America will experience one of these rare occurrences, as a total eclipse will start over the South Pacific Ocean before crossing Mexico, the United States, and Canada. The event will pass through the continent in just an hour and 35 minutes.

Mexico’s Pacific coast will be the first part of continental North America that will witness totality, around 11:07 a.m. PDT. The eclipse will then enter the US through Texas, moving to Oklahoma, Arkansas, Missouri, Illinois, Kentucky, Indiana, Ohio, Pennsylvania, New York, Vermont, New Hampshire and Maine. Some parts of Tennessee and Michigan will also be able to view the event.

The next total solar eclipse that will be visible to the Earth will occur twenty years from now, on August 23, 2044, according to NASA. Once more, parts of the US will be fortunate, and will be on the trajectory of the event.