Stratosphere

Aerosols – Climate

The role of stratospheric aerosols on climate is well known, even when the stratosphere is not affected by a major eruption as the Pinatubo. The variability of the aerosol content of the stratosphere must be quantified and the mechanisms controlling it characterized in order to take into account the contribution of these aerosols in Chemistry-Climate models, both for past studies and for projections. These scientific objectives are addressed by a strategy of synergy between observation and modelling. The variability of aerosols is determined by regular measurements under meteorological balloon with LOAC counters associated with available or future space observations (Lidar CALIOP/Calipso, EarthCARE, OMPS, SAGEIII). The radiative impact of aerosols at different spatial (regional, synoptic and global) and temporal (seasons, years) scales is studied by the WACCM community Chemistry-Climate model implemented at LPC2E. Particular attention is paid to key regions in terms of aerosol sources and/or precursors: the tropics, the polar vortex and the Asian monsoon. First, a focus is placed on the effect of regular “moderate” volcanic eruptions on the radiative balance through the direct injection of SO2 into the stratosphere, with the major eruption of Pinatubo as a point of comparison. Secondly, the contribution of biomass fires (pyroconvection episodes) and pollution sources (particularly in Asia) is particularly monitored by balloon and space measurements. Also, the impact of space-based materials is studied through collaborations with planetologists. In our strategy, the role of observations is dual because the models (WACCM, Reprobus of LATMOS) are both initialized and evaluated by these data.

Chemistry – Climate

Establishing and monitoring the balance of halogens (X=Cl, Br), water vapour and nitrogen in the stratosphere is a priority theme given the importance of these compounds to the radiative balance and the destruction of stratospheric ozone.

 

  • Halogen balance :

LPC2E is involved in the study of ozone destruction precursors such as BrO or source species or halogen reservoirs such as HCl. The study of the transport in equatorial regions of source species such as very short-lived species (VSLS; CHBr3 or CH2Br2) within the framework of the  European FP7 SHIVA project is studied by modelling (CCATT-BRAMS) or by using transport tracers such as CO measured by SPIRIT. Concerning halogen reservoirs, SPECIES, following SPIRALE, will be still for some time the only instrument in the world measuring in situ and with an ultra-high vertical resolution (a few meters) the main chlorine reservoir in the stratosphere, HCl. This information will be very important in the coming period of the absence of a dedicated stratospheric satellite.

 

  • Water vapour balance :

In the lower stratosphere, HOx radicals, originating mainly from water vapour, play a major role in ozone destruction cycles. The study of the H2O balance in the Upper Troposphere – Lower Stratosphere (UTLS) and the stratosphere and the processes that control its variability is conducted in particular by balloon-borne frost point hygrometers. The strategy consists in characterizing the key areas of water vapour entry into the stratosphere or dehydration of air masses (monsoon, tropics), and validating spatial measurements. The oxidation of methane contributes half to the production of stratospheric water vapour and so, combining measurements of SPECIES for CH4 and hygrometers during the same flights are a major asset to establish the balance of H2O and HOx. Similarly, through its H2O2 and HCHO measurements, SPECIES can also help to answer the crucial and still unresolved question of the origin of HOx radical sources other than CH4 and H2O.

  • Nitrogen balance :

Nitrogen oxides (NOx) take over from the chain destruction of ozone in the middle stratosphere. With this respect, we will reduce uncertainties about natural and anthropogenic sources of N2O, which will become the future main source of ozone-depleting species (NOx) during this century, by measuring its emissions from ground and vertical abundances from the surface to the stratosphere using the SPECIES instrument and exploiting the results of SPIRALE and SPIRIT (soil & aircraft), associated with chemistry- climate modelling (WACCM). This project is carried out in collaboration with ICARE (CNRS Orléans) and Colorado State University (Prof. A.R. Ravishankara).