The poles play a critical role in the radiative balance of the Earth. Roughly three times more energy is emitted than is absorbed at the extreme latitudes, which makes the changes in the atmosphere in these regions particularly impactful. In constraining the radiative balance, the largest variation and uncertainty in our current understanding comes from the abundance of clouds. Clouds provide both a cooling effect due to their reflectivity, but oppositely also prevent energy from escaping the planet by their greenhouse effect. The net contribution of clouds to the entire Earth’s radiative balance is a net cooling, but local variations are relevant and understudied, particularly around the poles. Part of the difficulty lies in measurements in these areas.
Remote observations offer the best pathway to constrain the abundances and radiative characteristics of clouds. In reflected light (wavelengths of 0.3 – 2.5 μm), one may be able to constrain the abundance, the type of clouds, and the cloud top height. Measurements over the surfaces with high albedo are typically challenging though and few can study the poles directly. In infrared wavelengths (3-50 μm) emission from the Earth and its atmosphere can be measured. Aside from the most important greenhouse gases, the cloud top height can be easily traced as it determines the emission temperature of the atmosphere.
The PREFIRE mission, launched in 2024, consists of two polar orbiting infrared observatories, and measures the emission spectrum of the Earth between 3.7 and 54 μm, providing near-continuous cover of the entire planet. As the two orbiters trail each other by several hours, short-term changes can be traced. By ingesting the relevant atmospheric parameters from the European Centre for Medium-Range Weather Forecasts, the radiative balance of the Earth can be simulated using radiative transfer tools, such as the Planetary Spectrum Generator. In Figure 2, preliminary results are shown, simulating the emission over two locations, one tropical and clear sky (Sassandra, Ivory Coast), and one clouded (Oslo, Norway).
For this project, the cloud cover over the Arctic will be studied using the PREFIRE satellite data and the radiative transfer tool the Planetary Spectrum Generator (PSG). Ultimately, this will advance understanding of the radiation balance of the fastest-warming region of the planet, referred to as the “Earth’s thermostat”.
The prospective candidate should have a strong background in programming and be familiar with the relevant background information.
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