photo #4325296

While aboard the International Space Station in 2022, on NASA’s Expedition 67, Italian astronaut Samantha Cristoforetti spotted these Cirrus clouds over Algeria, North Africa. Cirrus are high clouds composed entirely of ice crystals. While it might seem counterintuitive that ice can form in the heat of the day over the Sahara Desert, these high clouds will likely have formed up at altitudes of around 6 miles (10km), where air temperatures are typically -40°C. Not only this, but the desert may well be actively helping the Cirrus clouds form. Some of the smallest dust particles swept up from the sands below can be elevated right up into the high troposphere. There, the microscopic airborne particles can act as icing nuclei onto which moisture freezes to form ice crystals. In this way, some of the finest Saharan dust likely serves as the seeds that encourage ice crystals to grow and make high clouds. Sweeping joyfully across the Sahara, this extreme-altitude cloudspotter’s Cirrus clouds marked a milestone. Cristoforetti was the first European woman to be commander of the International Space Station.