Abstract: This work presents measurements of time-resolved mass-independently fractionated sulfate of volcanic origin from Antarctic ice core records that cover the last 2,600 years. These measurements are used to evaluate the time dependence of the deposited isotopic signal and to extract the isotopic characteristics of the reactions yielding sulfate from stratospheric volcanic eruptions in the modern atmosphere. Time evolution of the signal in snow (years) with respect to the fast SO2 oxidation in the stratosphere suggests that photochemically produced condensed phase is rapidly and continuously separated from the gas phase and preserved during transportation and deposition on the polar ice cap. On some eruptions, a nonzero isotopic mass balance highlights that a part of the signal can be lost during transport and/or deposition. The large number of volcanic events studied allows the ?33S versus ?36S and ?34S versus ?33S slopes to be constrained at ?1.56 (1? = 0.25) and 0.09 (1? = 0.02), respectively. The ?33S versus ?36S slope refines a prior determinations of ?36S/?33S = ?4 and overlaps the range observed for sulfur seen in early Earth samples (Archean). In recent volcanogenic sulfate, the ?33S versus ?34S differs, however, from the Archean record. The similitude for ?36S/?33S and the difference for ?33S/?34S suggest similar mass-independently fractionated sulfate processes to the Archean atmosphere. Using a simple model, we highlight that a combination of several mechanisms is needed to reproduce the observed isotopic trends and suggest a greater contribution from mass-dependent oxidation by OH in the modern atmosphere.

Abstract: This work investigates the impact of Forbush decrease (FD) and ground-level enhancement (GLE) in the atmosphere, based on solar and galactic cosmic-ray models and the extensive air shower simulations. This approach gives the possibility to investigate both the dynamic behavior of neutron monitors (NM) (using response function) and the flight dose. The ambient dose equivalent during quiet solar activity and solar events (i.e., FDs and GLEs) were investigated for realistic flight plans issued from the Eurocontrol Demand Data Repository. The calculated ambient dose equivalents were compared with flight measurements in quiet solar conditions; comparisons are relevant and demonstrate the ability to estimate the dose level. The GLE model was validated for the GLEs 5 and 69 using the cosmic-ray variation recorded by NMs. The GLE model was applied to flight dose calculations. All of these results show that dose values vary drastically with the route path (latitude, longitude and altitude) and with the delay between the flight departure and the solar event occurrence. Doses induced by extreme GLE events were investigated specifically for London to New York flights, and resulting additional doses are a few hundred or 1,000 ?Sv, impacting significantly the annual effective dose. This highlights the importance of monitoring extreme solar events and using realistic semi-empirical and particle transport methods for reliable calculation of dose levels.

Abstract: This work evaluates the IASI CO product against independent in-situ aircraft data from the MOZAIC program and the POLARCAT aircraft campaign. The validation is carried out by analysing the impact of assimilation of eight months of IASI CO columns retrieved for the period of May to December 2008 into the global chemistry transport model LMDz-INCA. A modelling system based on a sub-optimal Kalman filter was developed and a specific treatment that takes into account the representativeness of observations at the scale of the model grid is applied to the IASI CO columns and associated errors before their assimilation in the model. Comparisons of the assimilated CO profiles with in situ CO measurements indicate that the assimilation leads to a considerable improvement of the model simulations in the middle troposphere as compared with a control run with no assimilation. Model biases in the simulation of background values are reduced and improvement in the simulation of very high concentrations is observed. The improvement is due to the transport by the model of the information present in the IASI CO retrievals. Our analysis also shows the impact of assimilation of CO on the representation of transport into the Arctic region during the POLARCAT summer campaign. A considerable increase in CO mixing ratios over the Asian source region was observed when assimilation was used leading to much higher values of CO during the cross-pole transport episode. These higher values are in good agreement with data from the POLARCAT flights that sampled this plume.