Tracking N₂O from space: the contribution of the IASI satellite and the TN2OR algorithm
The Toulouse N2O Retrieval (TN2OR) combines the Radiative Transfer for TIROS Operational Vertical Sounder (RTTOV) model with the Levenberg–Marquardt optimal estimation method (OEM) to retrieve primarily nitrous oxide (N2O) from IASI on a global scale. The spectral band is focussed around 1300 cm-1 where both N2O and CH4 can be estimated simultaneously. This version is based on a fixed a priori N2O profile, making the retrieval independent of model priors. In addition, retrieval errors and averaging kernels are provided to characterize the N2O data. The TN2OR/IASI vertical profiles of N2O are retrieved from cloud-free spectral radiances observed by IASI over both land and sea during daytime and night-time.
The vertical sensitivity of the N2O profiles is around 300 hPa but, on some favourable conditions (e.g., high thermal contrast), it can reach 500 hPa. Maxima in N2O at 300 hPa are found, whatever the season considered, above Central Africa, a region combining both high surface N2O emissions and high convective activity, bringing rapidly elevated amounts of N2O from the surface to the upper troposphere. An example of the N2O distribution at 300 hPa for the month of July 2011 is presented Figure 1.
Figure 1: Monthly N2O distribution (left) and daily (right) at 300 hPa provided by TN2OR/IASI on a horizontal grid of 1°´ 1°.
N2O profiles (and CH4 profiles) are available for METOP-A for years 2011, 2019 and 2020 and accessible here
Contact : Jean-Luc Attie jean-luc.attie@utoulouse.fr
