Cold air outbreak in amazing detail

The current cold air outbreak, the first proper one this winter (see previous post), reveals incredible small-scale structure in the satellite image below. The land in the upper middle part of the picture is the Svalbard archipelago in the Northeast Atlantic.Image

The resolution of the original image (which you can see by clicking on the image above or go here) is 500 metres, which means that each pixel in the image is 500 metres wide. For maximum detail, check out this image at a resolution of 250 metres. There are so many things to see in the image, but here are some of the highlights.

In the upper left part of the picture, the white tendril-like features are sea ice. We also see some large floes. It’s all being blown southwards and at the same time broken up by the strong surface winds.

The north-south-oriented stripes that are made up of individual white dots are what we call cloud streets. They only occur when there’s a lot of convection (rising air) going on, and the dots themselves are cumulus clouds. Further south, away from the sea ice edge, the convection becomes less intense, and the cumulus clouds merge together into large patches of stratocumulus clouds. Cloud streets are a tell-tale sign of strong surface winds.

Downstream from Svalbard and in the lower part of the picture, the clouds get organized into a vortex. This is because there’s a small low-pressure system there, and the air starts to move in spiral-like, anti-clockwise patterns around the low (because of the earth’s rotation and the Coriolis force). The beautiful pattern we see in the image is, in other words, a polar low. Not a big one, but a polar low nonetheless.

Another interesting thing in the image are the wave clouds over and downstream from Svalbard. They form because the air moves over the mountains, much in the same way that waves form when water in a river hits rocks.

If you want to see more images from this region, take a look at NASA’s Hornsund subset.


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