New strategies for vertical transport in chemistry transport models: application to the case of the Mount Etna eruption on 18 March 2012 with CHIMERE v2017r4

Abstract

Abstract. Excessive numerical diffusion is one of the major limitations in the representation of long-range transport by chemistry transport models. In the present study, we focus on excessive diffusion in the vertical direction, which has been shown to be a major issue, and we explore three possible ways of addressing this problem: increasing the vertical resolution, using an advection scheme with anti-diffusive properties and more accurately representing the vertical wind. This study was carried out using the CHIMERE chemistry transport model for the 18 March 2012 eruption of Mount Etna, which released about 3 kt of sulfur dioxide into the atmosphere in a plume that was observed by satellite instruments (the Infrared Atmospheric Sounding Interferometer instrument, IASI, and the Ozone Monitoring Instrument, OMI) for several days. The change from the classical Van Leer (1977) scheme to the Després and Lagoutière (1999) anti-diffusive scheme in the vertical direction was shown to provide the largest improvement to model outputs in terms of preserving the thin plume emitted by the volcano. To a lesser extent, the improved representation of the vertical wind field was also shown to reduce plume dispersion. Both of these changes helped to reduce vertical diffusion in the model as much as a brute-force approach (increasing vertical resolution).

Stratospheric aerosol layer perturbation caused by the 2019 Raikoke and Ulawun eruptions and their radiative forcing

“…Elevated AOD values in the NH in January 2020 (Fig. 4h) point to polar stratospheric clouds related to the strong Arctic stratospheric vortex in winter 2020 (Lawrence et al, 2020).…”

The CHIMERE v2020r1 online chemistry-transport model

“…This is a way to ensure mass-flux consistency and therefore the conservation of mass and mixing ratio. However, as discussed in Lachatre et al (2020), this approach introduces large errors in upper tropospheric wind, and, it is possible to use directly the vertical wind speed w from the forcing meteorological model and compensate the errors in mixing ratio introduced thereby, even though this introduces errors in mass conservations.…”

“…is_diagwinw=1 corresponds to the original CHIMERE formulation, is_diagwinw=0 to the approach desscribed in Lachatre et al (2020). • idiagblh: A diagnostic report of the Boundary Layer Height (BLH) has been available in CHIMERE for many versions.…”

“…Reduction on the positive ozone bias close to the ground could be linked to the antidiffusive properties of the Després and Lagoutière (1999) scheme, reducing erroneous downward transport of ozone from the higher troposphere which has been shown by, e.g., Emery et al (2011), to be a major source of overestimation of ozone concentration in the midlatitudes. Implementation of the Després and Lagoutière (1999) scheme in CHIMERE is discussed in detail in Lachatre et al (2020), which shows the strong reduction in vertical diffusion obtaine with the use of this scheme relative to Van Leer (1977). Mailler et al (2021) discusses in more detail the strength and weaknesses of this scheme relative to Van Leer (1977).…”

“…5. Vertical transport: updated strategy for the vertical advection of pollutants and the implementation of the Després and Lagoutière (1999) antidiffusive advection scheme, evaluated in Lachatre et al (2020).…”