What does this mean?

The maps and bar graphs show how the amount of water vapor in the Arctic atmosphere for different years and months compares to averages from 1979 to 2013. On the map, areas with greater than average water vapor for the selected month and year are indicated in purples (positive anomalies), and areas with less than average water vapor are shown in greens (negative anomalies). The values show the mass of water vapor in a column of the atmosphere that stretches from the surface to the top of the atmosphere.

The bar graph indicates the water vapor anomaly for the selected month and year, for the entire Arctic (the area north of 70°N). Continue reading...