There is a very famous saying that atmospheric scientists like myself learned along the way in our undergraduate or graduate studies. It goes,
Big whorls have little whorls, That feed on their velocity; And little whorls have lesser whorls, And so on to viscosity.
In modern translation, "whorls" is often replaced with "whirls." The saying is attributed to noted meteorologist and mathematician Lewis Frye Richardson. He is a pioneer of modern weather forecasting. Richardson was driven by a desire to use the laws of physics to predict how the atmosphere changes. This fact was a central to his important work on finite differencing methods, a technique for putting complex equations in format that the earliest computers could handle. The rhyming quote from Richardson, appearing in his classic Weather Prediction by Numerical Processes text, captured his postulation that cascading levels of turbulence that ultimately dissipate at the smallest scale described atmospheric processes. Upon first glance at the image below, I thought it was swirling mass of clouds, but then I realized that it was sea ice. Why is sea ice swirling?
The swirls were first brought to my attention in a Tweet this week by doctoral candidate and cryospheric-climate expert Zack Labe. He tweeted "high pressure over the Beaufort Sea (#Arctic) is allowing for clear satellite views this week of the gorgeous swirling sea ice along the ice edge." By the way, Zach acquired this incredible image using the NASA Worldview website. If you are not familiar with it and want to explore our Earth from the vantage point of space, I highly recommend it. I gave an assignment to my freshman seminar class at the University of Georgia, and the students were blown away by Worldview, but I digress. Let's talk sea ice swirls because I was immediately curious as a scientist and someone that just thought they looked cool. And speaking of cool, check out this animated GOES satellite loop from April 2017 shared with me by NOAA weather satellite Dr. Dan Lindsey. You will see the sea ice swirls (relatively stationary) compared to the cloud motion.
Before I discuss sea ice swirls, it is useful to discuss the "sea ice cycle." The NASA Earth Observatory website describes it this way:
Each year, Arctic sea ice grows through the winter, reaching its maximum extent around March. It then melts through the summer, reaching its minimum in September. By October, Arctic waters start freezing again.
In the image above, swirls of sea ice can be seen along the east coast of Greenland. The Fram Strait is a well-known passageway for sea ice transiting from the Arctic Ocean. Over the years and with warming temperatures, scientists have found less thick sea ice and therefore less Arctic sea ice volume. The Beaufort Gyre is a wind-driven current in the Arctic Ocean that regulates sea ice formation and climate in the northern polar region. NASA's website suggests that the "fence" or sea-ice trapping mechanism of the Beaufort Gyre has been disrupted in recent decades. Specifically, it says
until the late 1990s, ice would persist in the Gyre for years, growing thicker and more resistant to melt. Since the start of the twenty-first century, however, ice has been less likely to survive its trip through the southern part of the Beaufort Gyre. As a result, less Arctic sea ice has been able to pile up and form multi-year ice.
Sea ice swirls are found throughout the Arctic Beaufort Gyre region. Why do they swirl? In the NOAA Suomi NPP satellite image from March 8, 2018 (below), sea ice swirls are observed off the Canadian coast near the Labrador and Newfoundland provinces. At first glance, it is easy to think you are looking at swirling clouds, however, it is indeed swirling eddies (or whirls) of sea ice. Ocean currents and off-shore wind patterns can organize the chunks of ice into swirls ranging from several hundred feet to hundreds of miles in diameter, according to NOAA. It is not by accident that every example that I used in this discussion was from the fall or spring months. At these times, the sea ice is warm enough to fragment but cold enough to remain frozen as it moves about in the ocean current. Due to differences in water density, such eddies will often form along boundaries of cold and warm currents.
As I close, check out the NASA perpetual ocean animation at this link. It is a fascinating look at big whirls, little whirls, and everything in between.
