Retrieval of Metop-A/IASI N2O Profiles and Validation with NDACC FTIR Data

International audienceThis paper reports atmospheric profiles of N2O retrieved from Metop/IASI with the Software for the Retrieval of IASI Data (SOFRID) for the 2008–2018 period and their validation with FTIR data from 12 stations of the Network for the Detection of Atmospheric Composition Changes (NDACC). SOFRID retrievals performed in the 2160–2218 cm−1 spectral window provide 3 independent pieces of information about the vertical profile of N2O. The FTIR versus SOFRID comparisons display a better agreement in the mid-troposphere (MT, 700–350 hPa) than in the lower (LT, Surface–700 hPa) and upper (UT, 350–110 hPa) troposphere with correlation coefficients (R) in the 0.49–0.83 range and comparable variabilities (3–5 ppbv). The agreement for oceanic and coastal stations (R > 0.77) is better than for continental ones (R < 0.72). The SOFRID MT N2O mixing ratios are significantly biased high (up to 16.8 ppbv) relative to FTIR at continental stations while the biases remain below 4.2 ppbv and mostly unsignificant when oceanic data are considered. The average MT decadal trends derived from SOFRID at the 8 NDACC stations with continuous observations during the 2008–2018 period (1.05 ± 0.1 ppbv·yr−1) is in good agreement with the corresponding FTIR trends (1.08 ± 0.1 ppbv·yr−1) and the NOAA-ESRL trends from surface in-situ measurements (0.95 ± 0.02 ppbv·yr−1). In the Northern Hemisphere where they are clearly detected, the N2O MT seasonal variations from SOFRID and FTIR are phased (summer minima) and have similar amplitudes. SOFRID also detects the UT summer maxima indicating independent MT and UT information. The global MT N2O oceanic distributions from SOFRID display low geographical variability and are mainly characterized by enhanced tropical mixing ratios relative to mid and high latitudes

Transport of the 2017 Canadian wild fire plume to the tropics and global stratosphere via the Asian monsoon circulation

International audienceWe show that a fire plume originating at high northern latitudes during the Canadian wild fire event in July/August 2017 reached the tropics, and subsequently the stratosphere via the ascending branch of the Brewer-Dobson-Circulation (BDC). For this, we use a combination of aerosol extinction data from the Stratospheric Aerosol and Gas Experiment III (SAGEIII) and the Ozone Mapping Profiler Suite (OMPS), carbon dioxide measurements from the Infrared Atmospheric Sounding Interferometer (IASI), FLEXPART-TRACZILLA back-trajectories and information for the position and strength of the Asian Monsoon Anticyclone (AMA) transport barrier from the Chemical Lagrangian Model of the Stratosphere (CLaMS). The transport from high to low latitudes in the upper troposphere and lowermost stratosphere was mediated by the anticyclonic flow of the Asian monsoon circulation. The Canadian fire plume reached the Asian monsoon area in late August/early September, when the AMA was still in place. While there is no evidence of systematic mixing into the center of the AMA, we show that a substantial part of the Canadian fire plume is entrained into the circulation at the AMA edge, and is transported into the tropical UTLS, and possibly the Southern Hemisphere particularly following the North-South flow on the eastern side. In the tropics the fire plume is lifted by about 1.5 km per month. Inside the AMA we find evidence of the Asian Tropopause Aerosol Layer (ATAL) in August, doubling background aerosol conditions with a top of the atmosphere shortwave radiative forcing of -0.05 W/m2. This is estimated using the UVSPEC radiative transfer model and the LibRadtran package. The regional climate impact of the fire signal in the wider Asian monsoon area in September exceeds the impact of the ATAL by a factor of ∼3 (-0.13W/m2). Once in the stratosphere, the climate impact of such kind of trans-continental transported plumes can be hemispheric and long-lasting, pointing at the importance of this long-range dynamical interconnection of pollution sources

Quantifying the tropospheric ozone radiative effect and its temporal evolution in the satellite era

International audienceUsing state-of-the-art satellite ozone profile products, and chemical transport model, we provide an updated estimate of the tropospheric ozone radiative effect (TO3RE) and observational constraint on its variability over the decade 2008–2017. Previous studies have shown the short-term (i.e. a few years) globally weighted average TO3RE to be 1.17±0.03 W/m2, while our analysis suggests that the long-term (2008–2017) average TO3RE to be 1.21–1.28 W/m2. Over this decade, the modelled/observational TO3RE linear trends show negligible change (i.e. ±0.1 %/year), so the tropospheric ozone radiative contribution to climate has remained stable with time. Two model sensitivity experiments fixing emissions and meteorology to one year (i.e. start year – 2008) show that ozone precursor emissions (meteorological factors) have had limited (substantial) impacts on the long-term tendency of globally weighted average TO3RE. Here, the meteorological variability in the tropical/sub-tropical upper troposphere is dampening any tendency in TO3RE from other factors (e.g. emissions, atmospheric chemistry)

Quantifying the tropospheric ozone radiative effect and its temporal evolution in the satellite-era

Using state-of-the-art satellite ozone profile products, and chemical transport model, we provide an updated estimate of the tropospheric ozone radiative effect (TO3RE) and observational constraint on its variability over the decade 2008–2017. Previous studies have shown the short-term (i.e. a few years) globally weighted average TO3RE to be 1.17±0.03 W/m2, while our analysis suggests that the long-term (2008–2017) average TO3RE to be 1.21–1.28 W/m2. Over this decade, the modelled/observational TO3RE linear trends show negligible change (i.e. ±0.1 %/year), so the tropospheric ozone radiative contribution to climate has remained stable with time. Two model sensitivity experiments fixing emissions and meteorology to one year (i.e. start year – 2008) show that ozone precursor emissions (meteorological factors) have had limited (substantial) impacts on the long-term tendency of globally weighted average TO3RE. Here, the meteorological variability in the tropical/sub-tropical upper troposphere is dampening any tendency in TO3RE from other factors (e.g. emissions, atmospheric chemistry)