Nacreous Clouds Over Colorado
December 22, 2006
The photo above shows a breath-taking display of nacreous clouds at sunset over the continental divide in Colorado. It was taken on October 28, 2006, near Estes Park, Colorado. I initially thought these were lenticular clouds, then noctilucent clouds, but finally realized that this phenomenon better matches the description of nacreous clouds. They're rarely seen at mid latitudes. Nacreous clouds form at 15-25 km (9-16 miles) above the Earth's surface -- high in the stratosphere and well above tropospheric clouds. They're iridescent, sometimes referred to as mother-of-pearl clouds, but they aren't detached corona as are the much more common place iridescent clouds, and they seem to move considerably slower than clouds at lower altitudes. Nacreous clouds occur mostly, but not exclusively, during the winter months in polar regions; Scandinavia, Alaska, and Antarctica. They shine brightly in high altitude sunlight for upwards of two hours after ground level sunset or before dawn. Their unbelievably bright iridescent colors make them an unmistakable and unforgettable sight.