Meteoric Influences on Stratospheric Aerosol and Clouds (MeteorStrat)

Firstly, recent in-situ observations have confirmed findings from the late 1990s that most particles in the stratospheric aerosol layer contain refractory core of meteoric origin, posing a major challenge to the current generation of interactive stratospheric aerosol models. Secondly, how the polar stratospheric clouds, that provide the medium by which emissions of compounds such as CFCs leads to polar ozone loss, form in the Arctic has remained a persistent uncertainty, limiting the confidence of model predictions for how the ozone layer will recover. The MeteorStrat team have made two breakthrough research findings that uniquely enable to address long-standing questions in stratospheric aerosol and PSC science. Firstly, our global model "meteoric smoke interaction experiments" show major effects from extra-terrestrial material, the meteoric inclusions radically altering the vertical distribution of sulphuric particles, challenging how models predict changes in the stratospheric aerosol layer. Secondly, our laboratory PSC freezing experiments reveal that rather than ablation-generated smoke particles (which were found to be poor NAT nuclei), it is an inclusion of non-ablated meteoric fragment particles that may explain how many NAT particles nucleate in the Arctic. This project builds on these exciting research findings with two hypotheses addressing the overarching aim to assess how cosmic dust influences the composition of the stratosphere. A. That meteoric-sulphuric particles are larger, with shorter stratospheric residence times,
has important consequences for how models predict decay from volcanic enhancement
B. The mechanism by which solid nitric acid PSCs form in the Arctic can finally be explained
by the non-ablated meteoric fragments providing the preferential NAT nuclei

We will combine our internationally-leading laboratory and modelling capabilities to test these hypotheses. Our workplan addresses the following 5 related science questions:

1. How far do the high-latitude source meteoric-sulphuric particles extend to lower latitudes and
how variable is their mid-latitude abundance across different seasons and years? 2. Do the larger meteoric-sulphuric particles effect a faster volcanic decay timescale and if so
what are the implications for the surface cooling attributed to volcanic eruptions? 3. What is the source flux and size distribution of the non-ablated "meteoric fragment" input
and how do smoke or fragments transform into Junge layer meteoric-sulphuric particles? 4. How do the distinctly composed meteoric fragments facilitate NAT freezing and what are the
implications of the laboratory findings compared to smoke-driven parameterizations? 5. Can meteoric influence explain observed PSCs and how is Arctic ozone loss enhanced? A key philosophy of the project involves gathering in situ and satellite measurement datasets to ensure model predictions are observationally-constrained and calibrated to maximise confidence in research findings. The project will provide the UK Earth System Model with vital capability to simulate future changes to the stratosphere, in particular for the effects from volcanic and potential stratospheric sulphur or particle geoengineering.