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New insights into low-tropospheric temperatures in Antarctica

New insights into low-tropospheric temperatures in Antarctica

In contrast to lower latitudes, atmospheric temperature typically increases with altitude in Antarctica. The new study of FMI deepens the understanding on the structure and temporal variability of these temperature inversion layers based on observations from the Finnish research station, Aboa.

In polar regions, layers in which the air temperature increases with altitude, are common in the low troposphere. These temperature inversion layers have a significant impact on the Earth's surface energy balance and they affect, for example, the radiative fluxes in the atmosphere. Temperature inversions are a challenge for numerical weather prediction. In this new study, characteristics and temporal variations of temperature inversions were investigated in Dronning Maud Land, Antarctica. The study was based on vertical soundings measured using a tethered balloon at the Finnish research station Aboa during Antarctic summer 2010–2011. The soundings covered the lowest kilometre of the atmosphere. Generally, data on vertical structure of Antarctic atmosphere are scarce, but these new observations enabled to investigate diurnal variations of vertical structure with a good temporal and vertical resolution.

The study revealed that the near-surface temperatures and temperature inversions have notable diurnal variations in summer, despite the fact that the sun does not set below the horizon. Daytime heating is, however, not strong enough to destroy the entire inversion layer and, therefore, there often remains a long-living inversion layer, the lowest part of which strengthens during the nights. At lower latitudes, temperature inversions are mainly a night-time phenomenon. The study also showed that the temperature change with height within the inversion layer is very nonlinear; the majority of temperature change with height take place within the lowest 5–25 m, and in the thicker part of the inversion above the temperature change is small. Typically, the temperature increase is 1–8 degrees within the inversion layer. 

Temperature inversions are often formed due to radiative cooling at the surface, but their properties, such as strength and thickness, are strongly affected by vertical distribution of radiative- and heat fluxes. The study statistically demonstrated that strongest temperature inversions occur in early morning in weak wind conditions when the cloud fraction is also small. The results related to physical processes are, at least partly, valid for similar conditions elsewhere in Antarctica, but the relative contributions of the processes probably vary regionally.

More information:

Research scientist, Tiina Nygård, Tel: +358 29 539 3103, tiina.nygard@fmi.fi

Nygård, T., Tisler, P., Vihma, T., Pirazzini, R., Palo, T. and Kouznetsov, R. (2016), Properties and temporal variability of summertime temperature inversions over Dronning Maud Land, Antarctica. Q. J. R. Meteorol. Soc., doi:10.1002/qj.2951

 


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