High-resolution modelling of plume dispersion

Abstract

Climate change is one of the most important societal issues the world is currently facing. References 133Acknowledgements 147Unlike CO 2 , methane has a relatively short lifetime in the atmosphere of ≈ 9 years (Montzka et al., 2011). Consequently, immediate reduction in the total emissions can lead to a quick response in the abundance of atmospheric methane. To be able to cut the emissions, however, first the sources of methane should be identified and quantified. To help tackling this issue on the European scale, the MEthane goes MObile -MEasurements and MOdelling (MEMO 2 ) project started in 2017. The goal of the project was to combine measurement techniques used for fast identification and quantification of sources with state-of-art modelling techniques in order to help with the mitigation of methane emissions. The project comprised of over 20 academic and non-academic collaborators spread out over 7 countries. As also pointed out in Saunois et al. (2020), there are significant discrepancies in emission estimates from bottom-up techniques (measurements of local sources extrapolated to national scales), and top-down approach (atmospheric observations combined with inverse-modelling techniques). As the first goal, MEMO 2 aimed to tackle this problem by targeting local emissions from different where σ meand is the plume dispersion due to meandering, and σ relat is the relative dispersion contribution to the total plume growth. The relative contribution of each of these processes depends on the size of the plume itself. Very close to the source, where the plume is still narrow, meandering will be the dominant process, while further downwind, as the plume diameter L ϕ grows, the relative dispersion becomes dominant. The inset of Fig. 1.4 shows a turbulent energy spectra S(k) in relation to an instantaneous plume width L ϕ at some downwind location, highlighting the relationship of the plume size and 1.4 Plume dispersion: experiments and modelling 9 1.4.1 Experimental techniques Experimental research can be split into two categories, each with its advantages and disadvantages: laboratory studies in wind tunnels or water tanks and open field release experiments. The experiments in the former group mainly focused on elevated or ground releases into neutral surface flows (e.g. Fackrell & Robins, (1982a,b); Nironi et al. (2015); Eisma et al. ( 2018)). The advantage of these experiments is their reproducibility and the controlled setting that allows for research of fundamental drivers behind dispersion. Every aspect of these experiments is controllable and full profiles (vertical and horizontal) of plumes can be captured. Furthermore, the experiments can be run for extended periods of time and statistically significant datasets can be acquired. Therefore, this makes these experiments suitable for benchmarking the performance of numerical models. However, the idealized setting of laboratory experiments and the scale of motions being restricted by the size of the experiment itself, makes that these flows are rarely found i...