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Arctic Climate Research at the University of Illinois

Simulated Surface Air Temperature and Total Cloud Fraction Anomalies

Monthly maps of anomalies (wikipedia link) (differences from the climatological mean) of total cloud fraction and surface air temperature are shown for three years of a control-run simulation from the ECHAM5 global climate model (GCM). These images show the strong relationship between cloudiness and surface air temperatures in the Arctic.

Regions simulated as cloudier than normal (positive anomalies) are indicated as yellow and red in the top image, while fewer clouds than normal (negative anomalies) are displayed as shades of blue. Similarly, warmer temperatures than normal (positive anomalies) are illustrated as yellow and red in the bottom image, while colder temperatures (negative anomalies) are displayed as shades of blue.

Note in the animation that clouds have a positive impact on temperatures in the Arctic during the winter months. Positive cloud anomalies correspond to warmer surface temperatures, while clear sky anomalies (fewer clouds) correspond to regions of cooler than normal temperatures. In winter, clouds tend to trap the heat radiating from the earth and keep it in the lower atmosphere, rather than letting it radiate off into space. In contrast, clear skies permit full radiational cooling of the surface and cold temperatures are often experienced in a clear-sky Arctic.

The effect of clouds on surface air temperatures in summer is opposite to that in winter. Note in the animations how positive anomalies of clouds (cloudy conditions) tend to correspond to cooler regional surface air temperatures than normal while clear skies generally correspond to warmer surface conditions. Clouds in summer tend to block or reduce the amount of sunlight (solar radiation) reaching the surface. Less solar radiation reaching the surface during cloudy periods will result in cooler-than-normal surface air temperatures for cloudy regions/periods. In contrast, clear skies will permit more warming of the surface through increased surface absorption of solar radiation, and therefore, warmer surface air temperatures.

The unique night/day configuration of the Arctic (i.e., 24-hour summer daylight and 24-hour winter nights) exaggerate the opposing effects of clouds on surface air temperatures in the Arctic when compared to more southerly latitudes.