Nature can generate some perplexing patterns. Satellite images in April 2016, for example, showed mysterious lines crisscrossing the Caspian Sea. (It turns out those lines were caused by icebergs dragging their keels along the seafloor.) Now images from the coast of the Antarctic Peninsula show another curious phenomenon: what looks like a tendril of sea ice snaking away from the ice pack in the Weddell Sea.
On April 4, 2018, the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured this natural-color image of sea ice between various levels of cloud cover. As austral autumn progresses, sea ice around Antarctica is starting to grow again after reaching its annual minimum extent on February 20–21.
The long, isolated patch of ice is a curiosity that is not easily explained. “The sea ice edge is usually pretty far south this time of year,” said Ron Kwok, an ice scientist at NASA’s Jet Propulsion Laboratory. “I have never seen a coherent feature by itself like that in the middle of the ocean that survives without melting.”
Similar patterns show up in the atmosphere on the lee side of icebergs. These so-called “von Kármán vortex” streets arise when winds are diverted around a blunt, high-profile area—often an island rising from the ocean, or sometimes an iceberg. The alternating direction of rotation in the air forms swirls in the clouds.
Kelly Brunt, a glaciologist from NASA’s Goddard Space Flight Center and the University of Maryland, said she has seen snake-like patterns show up in the sea water trailing icebergs. “While it’s not sea ice, you can see corrupted von Kármán streets associated with the currents in the lee of an iceberg,” she said. The physical parameters that give rise to vortex streets in the air might similarly produce the pattern in sea water.
References and Related Reading
- NASA Earth Observatory (2017, August 13) Two Views of Von Kármán Vortices.
- National Snow & Ice Data Center (2018, April) Seasonal increase in Antarctic sea ice. Accessed April 13, 2018.
NASA Earth Observatory images by Joshua Stevens, using VIIRS data from LANCE/EOSDIS Rapid Response. Story by Kathryn Hansen.
- Suomi NPP - VIIRS