Reduced solar radiation during eclipses causes low-level clouds to melt away
If you’ve ever been lucky enough to witness a solar eclipse, you’ll certainly have been struck not only by the eery dimming of the light in the middle of the day, but also by the sudden chill in temperature. There have also been reports that just before totality, low-level clouds dissipate, raising the intriguing possibility that solar eclipses could also influence regional weather as the Moon’s shadow passes across Earth.
Victor Trees at the Royal Netherlands Meteorological Institute in De Bilt, and his colleagues, set out to investigate this effect. They turned to data from Earth observation satellites in geostationary orbit, which can provide imagery over large geographical areas, and focused on three solar eclipses between 2005 and 2016. They analysed the type of clouds present in the skies both immediately before and during each eclipse.
They found that even partial eclipses can indeed change the pattern of clouds: low-level cumulus clouds were observed to dissipate, whereas higher-altitude clouds were unaffected. And this effect on diminishing cloud cover happens even with only around 15 per cent of the Sun’s disc obscured. To drill down into what’s going on, they ran atmospheric simulations, which showed that the clouds start disappearing 15–20 minutes after the ground cools in the Moon’s shadow. This equates to the time it takes warm, moist air near the ground to rise to a cooler altitude where the water vapour condenses into cloud.
On the face of it, this might appear to be nothing more than a curious observation on the short-term effects of solar eclipses on cloud patterns. But, the study argues, this demonstration of just how sensitive low-level cloud cover is to even small reductions in the incident solar radiation could have profound implications.
Clouds are crucial
Climate change is already proceeding at an alarming rate, and if international efforts to limit greenhouse gas emissions are not successful
