Click on the video to find out what is possibly flying around in the eye of Arthur.
In the video, the left image is Irene and the right is Arthur near landfall. The color is indicating what the radar "saw" in the eye of these storms. So what is the pink and white color?
Rain? Hail? Sea Foam? Sand?
The latest radar technology allows us to measure objects based on their horizontal (length) and vertical (height) characteristics. Like trying to identifying a pineapple in complete darkness using only your hands, you know what it should feel like and can come to that conclusion after feeling around for a bit. The radar knows what rain should look like as well as hail, but when the pink and white colors show up the radar it is saying, "Here are the dimensions, but I can't identify the object".
Different shapes equal different colors on the radar display.
In the case of Arthur, the radar was identifying rain all around the eye of the storm but in the middle it was seeing something different. Specifically, the beam was coming back indicating an object that was longer than it was taller, thus the pink and white.
Based on a study done in 2012 on Irene and Sandy, it is entirely possible that we are seeing birds being trapped in the eye of Arthur. When you think about it from a birds perspective it makes sense. The calmest wind is in the eye, and once there it would take a lot of effort to escape through the turbulent weather (including 80+mph winds) swirling just a few miles away. In the bird's case, there is nothing let to do, but just keep flying, just keep flying.
Interestingly, it's not just radar data supporting this, but also witness accounts. A Cape Lookout Ranger said they found birds from Florida, the Bahamas and Caribbean on the NC coastline after Arthur.
I've had a couple of questions regarding how birds actually get caught in the circulation.
The thinking here is that the birds get "caught" in the circulation long before it is named or fully developed. I've read that birds in the Bahamas and such will begin to fly and before they know it, they're trapped in a tropical circulation.
You can think of it like this, say you were driving from Bath to Raleigh and discover halfway through the trip you have 100mph winds circulating around your car. Do you take the risk of exiting the interstate at Raleigh, busting through the violent weather or just keep driving with it...even if the circulation goes 200 miles past your original destination?
Here's a link to a fantastic study done on the subject prior to Arthur. One of the highlights in the paper was the analysis of how the bioscatter (birds) responded to changes in the physical shape of the eye. The study also shows a huge drop off in bird signatures right after landfall, because, let's be honest if you were flying for 4 days straight you would take a rest at the first sight of land too. Cool!