Abstract
In recent years, the interest has grown in satellite-derived hyperspectral radiance measurements for assessing the individual impact of climate drivers and their cascade of feedbacks on the outgoing longwave radiation (OLR). In this paper, we use 10 years (2008–2017) of reprocessed radiances from the infrared atmospheric sounding interferometer (IASI) to evaluate the linear trends in clear-sky spectrally resolved OLR (SOLR) in the range [645–2300] cm−1. Spatial inhomogeneities are observed in most of the analyzed spectral regions. These mostly reflected the natural variability of the atmospheric temperature and composition but long-term changes in greenhouse gases concentrations are also highlighted. In particular, the increase of atmospheric CO2 and CH4 led to significant negative trends in the SOLR of −0.05 to −0.3% per year in the spectral region corresponding to the ν2 and the ν3 CO2 and in the ν4 CH4 band. Most of the trends associated with the natural variability of the OLR can be related to the El Niño/Southern Oscillation activity and its teleconnections in the studied period. This is the case for the channels most affected by the temperature variations of the surface and the first layers of the atmosphere but also for the channels corresponding to the ν2 H2O and the ν3 O3 bands.
Highlights
The Earth’s climate is closely linked to the flow of energy in and out of the Earth-atmosphere system
For the sake of clarity, these are expressed as a percentage of the average spectrally resolved OLR (SOLR) in the year 2008
Note that the choice of the reference year matters very little for the calculation of trends, as the relative changes in SOLR are very small
Summary
The Earth’s climate is closely linked to the flow of energy in and out of the Earth-atmosphere system. In the wings of the CO2 bands and in the ν4 CH4 band, characterized by lower maximum sensitivity levels (~350–500 hPa), the negative LT in the tropics and at Northern hemispheric mid-latitudes (between 45°N and 30°S) reflect the increase in the CO2 and CH4 IR absorption which shifts the effective emitting level of radiations to higher (and substantially colder) altitudes of the troposphere[38,48,49].
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