 This typical pattern was blocked by a ridge of high pressure over Greenland, resulting in a negative Arctic oscillation, forming a kink in the jet stream and causing it to double back on itself off the East Coast; Sandy was caught up in this northwesterly flow.The blocking pattern over Greenland also stalled an arctic front, which combined with the cyclone.Mark Fischetti of "Scientific American" argued that the jet stream's unusual shape was caused by the melting of Arctic ice.