Winter-like weather has arrived in the northern hemisphere. But is this winter colder than past ones, or warmer? That is the question NASA seeks to answer with this latest visualization. They have taken temperature measurements using the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite. Then they compared the week of December 3-10, 2010 to the average of the same week from 2002 to 2009. Red indicates areas that are warmer than the average, and blues represent areas that are colder than the average. What caused Greenland and parts of Canada to be warmer than average, while northern Europe was cooler than normal? In short, it was the Arctic Oscillation.
The Arctic Oscillation is a climate pattern that influences winter weather in the northern hemisphere. It describes the relationship between high pressure in the mid-latitudes and low pressure over the Arctic. When the pressure systems are weak, the difference between them is small, and air from the Arctic flows south, while warmer air seeps north. This is referred to as a negative Arctic Oscillation. Like December 2009, the Arctic Oscillation was negative in early December 2010. Cold air from the Arctic channeled south around a blocking system over Greenland, while Greenland and northern Canada heated up.
