Under normal conditions, the temperature in the lowest layer of the atmosphere (the troposphere) decreases with height. The higher you go, the colder the temperature becomes. This is why there can be snow-capped mountains in warm climates. However, something quite different happens regularly in the Arctic during the non-summer months: the temperature increases with height! This is called a temperature inversion. This unusual phenomenon can also (not quite as extreme) occur in mid-latitudes. Temperatures eventually decrease as usual, but the existence of this inversion is very interesting.
We experience this temperature inversion almost every day while we are in the high Arctic at Eureka (Nunavut, Canada) for the Canadian Arctic ACE validation campaign. Due to the inversion, we experience much warmer temperatures (sometimes up to 20°C higher) at our research laboratory PEARL (the Polar Environment Atmospheric Research Laboratory), which is approximately 600 m (above sea level) higher than Eureka, which is at sea level. While our colleagues in Eureka are experiencing -50°C, those of us working at PEARL are often enjoying the relatively “warm” temperature of -30°C.
An example of the temperature above Eureka is shown in Figure 1 between the surface and 5 km during the winter, on 2 March 2013, and half a year earlier during the summer, on 30 August 2012. A strong inversion can be seen in the winter profile, where the temperature increases from the ground to almost 1 km in the winter by 20°C (from -50°C to -30°C). The temperature in the summer profile decreases normally with height.
This regular temperature inversion in the high Arctic is caused by the lack of surface heating by the Sun, which stays below the horizon during the winter (the Polar Night), and the continuous loss of heat from the surface (through emission of infrared radiation). This allows the temperatures near the surface to be colder than the air a few kilometers higher up. The infrared cooling of the surface is especially intense for dry and clear weather conditions, which occur regularly in the high Arctic.
What are the consequences?
Temperature inversions are very stable profiles, which stop convection in this layer. This means that there is almost no mixing of the air. Under these circumstances, emissions do not rise to higher altitudes. Pollutants from the surface can become trapped close to the ground.
Trapped smoke can be seen during strong temperature inversions at Eureka. For example, we saw a thick layer of smoke stuck above the station (see Figure 2) on 2 March 2013. Fortunately, apart from the power plant to generate electricity for the weather station, there are no other sources of pollutants near Eureka.
Figure 2: Picture of Eureka on 2 March 2013. The emitted smoke is trapped close to the ground.
More information on the temperature inversion, the weather in Eureka, and how they have changed over the last decades can be found in Lesins et al. (2010) for the technically-inclined.
– Debora Griffin
PhD student, University of Toronto