Libois, Quentin; Ivanescu, Liviu; Blanchet, Jean-Pierre; Schulz, Hannes; Bozem, Heiko; Leaitch, W. Richard; Burkart, Julia; Abbatt, Jonathan P. D.; Herber, Andreas B.; Aliabadi, Amir A. et Girard, Éric
(2016).
« Airborne observations of far-infrared upwelling radiance in the Arctic ».
Atmospheric Chemistry and Physics, 16(24), pp. 15689-15707.
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Résumé
The first airborne measurements of the Far-
InfraRed Radiometer (FIRR) were performed in April 2015
during the panarctic NETCARE campaign. Vertical profiles
of spectral upwelling radiance in the range 8–50 μm were
measured in clear and cloudy conditions from the surface up
to 6 km. The clear sky profiles highlight the strong dependence
of radiative fluxes to the temperature inversion typical
of the Arctic. Measurements acquired for total column water
vapour from 1.5 to 10.5mm also underline the sensitivity
of the far-infrared greenhouse effect to specific humidity.
The cloudy cases show that optically thin ice clouds increase
the cooling rate of the atmosphere, making them important
pieces of the Arctic energy balance. One such cloud exhibited
a very complex spatial structure, characterized by large
horizontal heterogeneities at the kilometre scale. This emphasizes
the difficulty of obtaining representative cloud observations
with airborne measurements but also points out
how challenging it is to model polar clouds radiative effects.
These radiance measurements were successfully compared
to simulations, suggesting that state-of-the-art radiative
transfer models are suited to study the cold and dry Arctic
atmosphere. Although FIRR in situ performances compare
well to its laboratory performances, complementary simulations
show that upgrading the FIRR radiometric resolution
would greatly increase its sensitivity to atmospheric and
cloud properties. Improved instrument temperature stability
in flight and expected technological progress should help
meet this objective. The campaign overall highlights the potential
for airborne far-infrared radiometry and constitutes a
relevant reference for future similar studies dedicated to the
Arctic and for the development of spaceborne instruments.
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