Atmospheric Chemistry and Physics
www.atmos-chem-phys.net
1680-7316
1680-7324
8
11
2008
10.5194/acp-8-2885-2008
http://www.atmos-chem-phys.net/8/2885/2008/
http://www.atmos-chem-phys.net/8/2885/2008/acp-8-2885-2008.html
http://www.atmos-chem-phys.net/8/2885/2008/acp-8-2885-2008.pdf
2885
2894
2008-06-06
Measurement of the water vapour vertical profile and of the Earth's outgoing far infrared flux
L. Palchetti
l.palchetti@ifac.cnr.it
G. Bianchini
B. Carli
U. Cortesi
S. Del Bianco
Istituto di Fisica Applicata "Nello Carrara" – Consiglio Nazionale delle Ricerche IFAC–CNR, Sesto Fiorentino, Firenze, 50019, Italy
Our understanding of global warming depends on the accuracy with
which the atmospheric components that modulate the Earth's radiation
budget are known. Many uncertainties still exist as regards the
radiative effect of water in the different spectral regions, among
which is the far infrared, where very few observations have been
made. An assessment is shown of the atmospheric outgoing flux
obtained from a balloon-borne platform with wideband
spectrally-resolved nadir measurements at the top of the atmosphere
over the full spectral range, from 100 to 1400 cm<sup>−1</sup>, made by a
Fourier transform spectrometer with uncooled detectors. From these
measurements, we retrieved 15 pieces of information regarding water
vapour and temperature profiles and surface temperature, with a
major improvement in our knowledge of water vapour in the upper
troposphere. The retrieved atmospheric state made it possible to
calculate the emitted radiance also at frequencies and zenith angles
that have not been observed and to determine the outgoing spectral
radiation flux. This proves that spectrally resolved observations
can be used to derive accurate information on the integrated flux.
While the retrieved temperature was in agreement with ECMWF
analysis, the retrieved water vapour profile differed significantly;
depending on the time and the location, the derived flux in the far
infrared (20–600 cm<sup>−1</sup>) differed by 2–3.5 W/m<sup>2</sup> from that
calculated using ECMWF. The error with which the far infrared flux
is determined by REFIR-PAD is about 0.4 W/m<sup>2</sup> and is caused
mainly by calibration uncertainties, while detector noise has a
negligible effect. This proves that uncooled detectors are adequate
for top-of-the-atmosphere radiometry.
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