Comparison between the assimilation of IASI Level 2 ozone retrievals and Level 1 radiances in a chemical transport model

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An upper tropospheric ‘ozone river’ from Africa to India during the 2008 Asian post-monsoon season

We have used ozone data from the Infrared Atmospheric Sounding Interferometer to follow an event of ozone-enriched air-masses in the upper troposphere from eastern Africa to northern India. The ozone transport (hereafter called ‘ozone river’ or O3R) occurred during the Asian post-monsoon season in 2008 and was associated with Rossby wave propagation. The persistence of the O3R in a narrow channel was confirmed by MOZAIC airborne data over the northwestern Indian coast. The regions of origin of the O3R were identified by a transport analysis based on the Lagrangian model FLEXPART. The Lagrangian simulations combined with potential vorticity fields indicate that stratospheric intrusions are not likely to be the most important contributor to the observed O3 enhancements. A high-resolution Eulerian model, Meso-NH, with tagged tracers was used to discriminate between African biomass burning, lightnings and Indian anthropogenic pollution as potential sources of precursors for the O3R. Lightning NOx emissions, associated with convective clouds over Africa, were found to be the principal contributor to the ozone enhancement over the Indian Ocean taking advantage of a northeastward jet. This case study illustrates African lightning emissions as an important source for enhanced O3 in the upper troposphere over the Indian Ocean region during the post-monsoon season

Source attribution of carbon monoxide and ozone over the Indian subcontinent using MOZART-4 chemistry transport model

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Observation of HD18O, CH3OH and vibrationally-excited N2O from Odin/SMR measurements

The sub-millimetre radiometer (SMR) instrument aboard the Odin satellite launched in February 2001 is dedicated to the observation of trace gas profiles in the stratosphere and in the mesosphere, in particular water vapour and its isotopic species HDO, H217O and H218O. By averaging more than 400 000 Odin/SMR spectra over the period from November 2002 to March 2003, weak lines have been detected in the atmosphere. These weak lines have been attributed to water isotopic species HD18O, to a vibrationally-excited N2O, and to CH3OH

Equatorial transport as diagnosed from nitrous oxide variability

International audienceThe mechanisms of transport on annual, semi-annual and quasi-biennial time scales in the equatorial (10° S-10° N) stratosphere are investigated using the nitrous oxide (N2O) measurements of the space-borne ODIN Sub-Millimetre Radiometer from November 2001 to June 2005, and the simulations of the three-dimensional chemical transport models MOCAGE and SLIMCAT. Both models are forced with analyses from the European Centre for Medium-range Weather Forecast, but the vertical transport is derived either from the forcing analyses by solving the continuity equation (MOCAGE), or from diabatic heating rates using a radiation scheme (SLIMCAT). The N2O variations in the mid-to-upper stratosphere at levels above 32 hPa are generally well captured by the models though significant differences appear with the observations as well as between the models, attributed to the difficulty of capturing correctly the slow upwelling associated with the Brewer-Dobson circulation

Tropical tropospheric ozone and carbon monoxide distributions: characteristics, origins, and control factors, as seen by IAGOS and IASI

International audienceThe characteristics and seasonal variability in the tropical tropospheric distributions of ozone (O3)and carbon monoxide (CO) were analysed based on in situ measurements provided by the In-service Aircraft for aGlobal Observing System (IAGOS) programme since 1994 and 2002, respectively, combined with observationsfrom the Infrared Atmospheric Sounding (IASI) instrument on board the MetOp-A satellite since 2008. TheSOFT-IO (SOft attribution using FlexparT and carbon monoxide emission inventories for In-situ Observationdatabase) model, which couples back trajectories with CO emission inventories, was used to explore the originsand sources of the tropical CO observed by IAGOS.The highest O3 and CO mixing ratios occur over western Africa in the lower troposphere (LT: surface to750 hPa) during the fire season (75 ppb of O3 at 2.5 km and 850 ppb of CO at 0.3 km over Lagos in January),mainly due to anthropogenic (AN) emissions and a major contribution from fires. The secondary maxima areobserved in Asia in the mid-troposphere (MT: 750–300 hPa) and upper troposphere (UT: 300–200 hPa) in Aprilfor O3 and in the LT in January for CO, with larger contributions from AN emissions. The lowest O3 and COmixing ratios occur over Caracas.In the tropical LT, the majority of the location clusters are affected by local and regional AN emissions. Thehighest AN impact is found over Asia, Arabia and eastern Africa, and South America (> 75 % of CO). Biomassburning (BB) emissions also originate from local or regional sources but with stronger seasonal dependence. Thehighest BB impact is found over southern tropical Africa (57 %–90 %), except in April, mostly due to local fires,but also from Northern Hemisphere Africa in January (45 %–73 %) and Southern Hemisphere South America inOctober (29 % over Windhoek).In the MT and UT, AN emissions are more important and dominate in the eastern part of the tropics (from theMiddle East to Asia). BB contributions are more important than in the LT, especially from the African fires inJanuary and July and from South East and equatorial Asia in April and October.The overall highest amount of CO is exported from Africa, with the main transport pathway from the dry-season African regions towards the wet-season ones. In contrast, the impact of the Asian emissions in the LTand MT is limited on a local or regional scale. The transport of polluted Asian air masses is important in the UTduring the Asian summer monsoon and post-monsoon seasons, when convection is activ

Tropospheric ozone from IASI: comparison of different inversion algorithms and validation with ozone sondes

Comparison of the inversion algorithms from LISA, LATMOS, LPMAA, and Eumesat: June 2007-August 2008. Comparison of the inversion algorithms from LISA and LA for 3 months: June 2008 – August 2008: 50 coincidences for 8 stations in the NH midlatitude

Tropospheric ozone from IASI: comparison of different inversion algorithms and validation with ozone sondes

Comparison of the inversion algorithms from LISA, LATMOS, LPMAA, and Eumesat: June 2007-August 2008. Comparison of the inversion algorithms from LISA and LA for 3 months: June 2008 – August 2008: 50 coincidences for 8 stations in the NH midlatitude

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

Transport of the 2017 Canadian wildfire plume to the tropics via the Asian monsoon circulation

International audienceWe show that a fire plume injected into the lower stratosphere at high northern latitudes during the Canadian wildfire event in August 2017 partly reached the tropics. The transport to the tropics was mediated by the anticyclonic flow of the Asian monsoon circulation. The fire plume reached the Asian monsoon area in late August/early September, when the Asian monsoon anticyclone (AMA) was still in place. While there is no evidence of mixing into the center of the AMA, we show that a substantial part of the fire plume is entrained into the anticyclonic flow at the AMA edge and is transported from the extratropics to the tropics, and possibly the Southern Hemisphere particularly following the north– south flow on the eastern side of the AMA. In the tropics the fire plume is lifted by ∼ 5 km in 7 months. Inside the AMA we find evidence of the Asian tropopause aerosol layer (ATAL) in August, doubling background aerosol conditions with a calculated top of the atmosphere shortwave radiative forcing of −0.05 W m−2. 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 2–4 and com-pares to that of a plume coming from an advected moderate volcanic eruption. The stratospheric, trans-continental trans- port of this plume to the tropics and the related regional cli- mate impact point to the importance of long-range dynamical interconnections of pollution sources