A Principal Components Analysis (PCA) of monthly MODIS Land Surface Temperature (LST) anomalies from 2001 to 2011 for the Arctic region. The first S-mode principal component (foreground) shows a distinctive spatial pattern associated with a rapidly oscillating temporal pattern (the blue line in the graph). To identify it, several well-known climate teleconnection indices were overlaid on the component (the green line on the graph). The overlaid index series uses the secondary axis and ETM also provides the option to invert the Y axis. This was done in this case to show that the first component is clearly the Arctic Oscillation (AO) – a coupled troposphere/stratosphere pressure pattern. Thus the AO can explain the greatest extent of variability in LST over this 10 year period. Note that when comparing index series such as the component and AO index in the graph, the comparison index can be slid back and forth to check for a lagged relationship. ETM indicates the lagged correlation when this is done.