Oliver Scharf

Bio: Oliver Scharf is an academic researcher from Université libre de Bruxelles. The author has contributed to research in topics: Wave function & Matrix (mathematics). The author has an hindex of 4, co-authored 4 publications receiving 200 citations.

FORLI radiative transfer and retrieval code for IASI

Abstract: This paper lays down the theoretical bases and the methods used in the Fast Optimal Retrievals on Layers for IASI (FORLI) software, which is developed and maintained at the "Universite Libre de Bruxelles" (ULB) with the support of the "Laboratoire Atmospheres, Milieux, Observations Spatiales" (LATMOS) to process radiance spectra from the Infrared Atmospheric Sounding Interferometer (IASI) in the perspective of local to global chemistry applications. The forward radiative transfer model (RTM) and the retrieval approaches are formulated and numerical approximations are described. The aim of FORLI is near-real-time provision of global scale concentrations of trace gases from IASI, either integrated over the altitude range of the atmosphere (total columns) or vertically resolved. To this end, FORLI uses precalculated table of absorbances. At the time of writing three gas-specific versions of this algorithm have been set up: FORLI-CO, FORLI-O3 and FORLI-HNO3. The performances of each are reviewed and illustrations of results and early validations are provided, making the link to recent scientific publications. In this paper we stress the challenges raised by near-real-time processing of IASI, shortly describe the processing chain set up at ULB and draw perspectives for future developments and applications.

Isotope shift in the sulfur electron affinity: Observation and theory

Abstract: The sulfur electron affinities ${}^{e}A$(S) are measured by photodetachment microscopy for the two isotopes $^{32}\mathrm{S}$ and $^{34}\mathrm{S}$ ($16$ $752.975$ 3(41) and $16$ $752.977$ 6(85) cm${}^{\ensuremath{-}1}$, respectively). The isotope shift in the electron affinity is found to be more probably positive, ${}^{e}A$($^{34}\mathrm{S}$)$\ensuremath{-} {}^{e}A$($^{32}\mathrm{S}$) $=+0.0023(70)$ cm${}^{\ensuremath{-}1}$, but the uncertainty allows for the possibility that it may be either ``normal'' [${}^{e}A$($^{34}\mathrm{S}$) $g {}^{e}A$($^{32}\mathrm{S}$)] or ``anomalous'' [${}^{e}A$($^{34}\mathrm{S}$) $l {}^{e}A$($^{32}\mathrm{S}$)]. The isotope shift is estimated theoretically using elaborate correlation models, monitoring the electron affinity and the mass polarization term expectation value. The theoretical analysis predicts a very large specific mass shift (SMS) that counterbalances the normal mass shift (NMS) and produces an anomalous isotope shift ${}^{e}A$($^{34}\mathrm{S}$)$\ensuremath{-} {}^{e}A$($^{32}\mathrm{S}$) $=\ensuremath{-}0.0053(24)$ cm${}^{\ensuremath{-}1}$, field shift corrections included. The total isotope shift can always be written as the sum of the NMS (here $+0.0169$ cm${}^{\ensuremath{-}1}$) and a residual isotope shift (RIS). Since the NMS has nearly no uncertainty, the comparison between experimental and theoretical RIS is more fair. With respective values of $\ensuremath{-}0.0146(70)$ cm${}^{\ensuremath{-}1}$ and $\ensuremath{-}0.0222(24)$ cm${}^{\ensuremath{-}1}$, these residual isotope shifts are found to agree within the estimated uncertainties.

On the fine structure photodetachment intensities using the irreducible tensorial expression of second quantization operators

Abstract: The branching ratios of the fine-structure photodetachment intensities of S- have been calculated by Blondel et al. (J. Phys. B 39(2006)1409) using the standard irreducible tensorial operator techniques. They observed that the relative intensities were consistent with the well known Engelking-Lineberger formula (Phys. Rev. A19(1979)149) derived from the fractional parentage approach, and qualified this agreement as remarkable. In the present paper, we show that it can be understood from a general interesting angular momentum expression relating a weighted sum of squared 9j-symbols and a weighted sum of products of squared 6j-symbols. We also point out that the standard approach result is a special case of the photodetachment cross sections parametrization by Pan and Starace (Phys. Rev. A47(1993)295) who already established the link with the Engelking-Lineberger's result. The present work provides a new, elegant and deep link between the two formalisms, thanks to the irreducible tensorial expression of the second quantization form of the electric dipole transition operator.

Tropospheric Ozone Assessment Report: Present-day distribution and trends of tropospheric ozone relevant to climate and global atmospheric chemistry model evaluation

Abstract: The Tropospheric Ozone Assessment Report (TOAR) is an activity of the International Global Atmospheric Chemistry Project. This paper is a component of the report, focusing on the present-day distribution and trends of tropospheric ozone relevant to climate and global atmospheric chemistry model evaluation. Utilizing the TOAR surface ozone database, several figures present the global distribution and trends of daytime average ozone at 2702 non-urban monitoring sites, highlighting the regions and seasons of the world with the greatest ozone levels. Similarly, ozonesonde and commercial aircraft observations reveal ozone’s distribution throughout the depth of the free troposphere. Long-term surface observations are limited in their global spatial coverage, but data from remote locations indicate that ozone in the 21st century is greater than during the 1970s and 1980s. While some remote sites and many sites in the heavily polluted regions of East Asia show ozone increases since 2000, many others show decreases and there is no clear global pattern for surface ozone changes since 2000. Two new satellite products provide detailed views of ozone in the lower troposphere across East Asia and Europe, revealing the full spatial extent of the spring and summer ozone enhancements across eastern China that cannot be assessed from limited surface observations. Sufficient data are now available (ozonesondes, satellite, aircraft) across the tropics from South America eastwards to the western Pacific Ocean, to indicate a likely tropospheric column ozone increase since the 1990s. The 2014–2016 mean tropospheric ozone burden (TOB) between 60˚N–60˚S from five satellite products is 300 Tg ± 4%. While this agreement is excellent, the products differ in their quantification of TOB trends and further work is required to reconcile the differences. Satellites can now estimate ozone’s global long-wave radiative effect, but evaluation is difficult due to limited in situ observations where the radiative effect is greatest.

Atmospheric ammonia and particulate inorganic nitrogen over the United States

Abstract: We use in situ observations from the Interagency Monitoring of PROtected Visual Environments (IMPROVE) network, the Midwest Ammonia Monitoring Project, 11 surface site campaigns as well as Infrared Atmospheric Sounding Interferometer (IASI) satellite measurements with the GEOS-Chem model to investigate inorganic aerosol loading and atmospheric ammonia concentrations over the United States IASI observations suggest that current ammonia emissions are underestimated in California and in the springtime in the Midwest In California this underestimate likely drives the underestimate in nitrate formation in the GEOS-Chem model However in the remaining continental United States we find that the nitrate simulation is biased high (normalized mean bias > = 10) year-round, except in Spring (due to the underestimate in ammonia in this season) None of the uncertainties in precursor emissions, the uptake efficiency of N2O5 on aerosols, OH concentrations, the reaction rate for the formation of nitric acid, or the dry deposition velocity of nitric acid are able to explain this bias We find that reducing nitric acid concentrations to 75% of their simulated values corrects the bias in nitrate (as well as ammonium) in the US However the mechanism for this potential reduction is unclear and may be a combination of errors in chemistry, deposition and sub-grid near-surface gradients This "updated" simulation reproduces PM and ammonia loading and captures the strong seasonal and spatial gradients in gas-particle partitioning across the United States We estimate that nitrogen makes up 15−35% of inorganic fine PM mass over the US, and that this fraction is likely to increase in the coming decade, both with decreases in sulfur emissions and increases in ammonia emissions

Advanced multiconfiguration methods for complex atoms : I. Energies and wave functions

Abstract: Multiconfiguration wave function expansions combined with configuration interaction methods are a method of choice for complex atoms where atomic state functions are expanded in a basis of configuration state functions. Combined with a variational method such as the multiconfiguration Hartree-Fock (MCHF) or multiconfiguration Dirac-Hartree-Fock (MCDHF), the associated set of radial functions can be optimized for the levels of interest. The present review updates the variational MCHF theory to include MCDHF, describes the multireference single and double process for generating expansions and the systematic procedure of a computational scheme for monitoring convergence. It focuses on the calculations of energies and wave functions from which other atomic properties can be predicted such as transition rates, hyperfine structures and isotope shifts, for example.