At least three, maybe even four, polar lows were active over the Barents Sea last night. Here’s a nice satellite image taken early Monday morning:
All of these are in the category of cyclones known as “comma clouds”, obviously because they look like inverted commas. As a side-note, maybe they should rather be called “apostrophe clouds”. Anyway, they are what we call baroclinic. That means that the low near the surface is linked to a trough higher up in the atmosphere, and these are not located on top of each other. This vertical structure allows the two lows to work together and to strengthen each other.
Most polar lows start out as baroclinic, but many of the develop a warm core and gradually enter a phase where they go from baroclinic to barotropic. Then the lows aloft and near the surface are locked in phase and no longer help each other grow. For the polar low to intensify in this stage, it needs to get its energy from the warm ocean surface.
This is how tropical cyclones (hurricanes) get their energy, too, and some polar lows are in certain ways similar to hurricanes. But so far all the research that has been done on “arctic hurricanes” has shown that the ocean surface is far too cold in the Arctic. In fact, we have a paper in review right now where we look at one such polar low.
Here’s another nice image of the current polar lows: