I have seen this picture, and this feature on the port fuselage called my attention. Does anybody know the purpose of this?
One of the features on this American Airlines Airbus A319 is the Gogo Inflight Internet.
The A319 will be the first aircraft type in American’s fleet to use Gogo’s ATG-4 Wi-Fi solution. ATG-4 uses more antennas and better data compression technology to provide more robust and reliable service (August 15, 2013).
There's another one on the other side. It's part of the air-to-ground (ATG) internet setup that utilizes Gogo's cellular towers in the US and Canada, as opposed to satellite internet.
Related external links:
Thanks to @mins for their help on the answer.