File:"Go!" in the clouds off the coast of Chile (MODIS 2022-05-15).jpg

English: In a letter to a friend dated January 14, 1843, Henry David Thoreau wrote, “You must not blame me if I do talk to the clouds…”. People have long been talking to, gazing at, and imagining seeing things in clouds as they look upward from Earth. These days, we can study the clouds by looking down on them from space—and the clouds themselves may sometimes seem to talk to us.

On May 6, 2022, a full 179 years after Thoreau admitted to cloud conversations, that the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Aqua satellite acquired a true-color image of a remarkable configuration of clouds off the coast of Chile, which seemed to be urging “Go!”. Maybe the clouds were sports fans, or—and much more likely—cloud and atmospheric conditions created patterns that, when combined with human imagination, appeared to create a word in the sky, just waiting to be captured by MODIS.

The Pacific Ocean off the coast of Chile is covered in large banks of cloud most of the time, and the region is famous for the formation of bizarre patterns. The dark, lacy swirl that forms the “G” is a type of open-cell cumulus pattern, while the thick white cloud is basically closed-cell marine stratocumulus. The dark breaks in the white cloud bank that appear to form the “o” and “!” are simply areas without cloud, allowing the dark waters of the ocean to show through and are most likely created by wind patterns.

Back in Thoreau’s day—actually until 1960 when NASA launched the first weather satellite—no one had noticed that clouds over the ocean frequently appeared to be formed in hexagonal cells with diameters ranging from 50 – 100 km (30-60 miles). These cell patterns are created by mesoscale cellular convection (MCC). In open cells, air is falling in the center of the hexagon and rising around the edges, so clouds formed at the edges, creating a lacy-looking pattern. In closed-cell clouds, air is rising in the center, so the hexagon is filled with fluffy cloud. There is also a third type of cloud formed by mesoscale cellular convection—an intermediate type with a radial structure that looks something like flowers or a wagon wheel. These are called actinoform clouds, derived from the Greek word “aktinos”, meaning “ray”. There are at least 2 actinoform clouds within the lacy open-celled cloud that makes up the “G”.