In this presentation I will explain an analysis of three different recovered remote-sensing measurements of the 1960s Northern Hemisphere mid-latitude stratospheric aerosol layer. Two of the datasets were recovered within student projects on the Leeds MRes in Climate and Atmospheric Science, the 3rd following a collaboration with Dr. Juan-Carlos Antuna Marrero (Univ. Valladolid, Spain) as part of a “data rescue activity” within the World Climate Research Program activity on stratospheric sulphur, SSiRC: http://www.sparc-ssirc.org/data/datarescueactivity.html Two of the datasets are for the 1963-1965 period when the tropical stratospheric reservoir was highly elevated following the two March 1963 Agung major eruptions (e.g. Niemeier et al., 2019): a series of searchlight measurements from White Sands, New Mexico during 1963 and 1964 (Elterman and Campbell, 1964; Elterman, 1966; Elterman et al., 1973), and the first ever multi-annual stratospheric aerosol dataset from the MIT lidar at Lexington, Massachussetts (Grams, 1966; Grams & Fiocco, 1967; Antuna Marrero et al., 2020). The 3rd dataset, from the 1966-67 period (after the Agung aerosol cloud had fully dispersed) is from two types of balloon measurements: a dust-sonde OPC (Rosen, 1964; Rosen, 1968) and solar-extinction-sounder (Rosen, 1969; Pepin, 1970) both balloon instruments measuring during a Sep 1966 field campaign in the tropics (Panama City, Panama) and a sustained set of NH mid-latitude measurements from Minneapolis, Minnesota in 1963-1967. The observations will be compared to interactive stratospheric aerosol model simulations in GA4 UM-UKCA of the Agung aerosol cloud (Dhomse et al., 2020) and new model experiments seeking to constrain the aerosol clouds from two VEI4 eruptions in Sep 1965 (Taal, Phillipines) and Aug 1966 (Awu, Indonesia).

The widespread presence of meteoric smoke particles (MSPs) within a distinct class of stratospheric aerosol particles has become clear from in-situ measurements in the Arctic, Antarctic and at mid-latitudes. We apply an adapted version of the interactive stratosphere aerosol configuration of the composition-climate model UM-UKCA, to predict the global distribution of meteoric-sulphuric particles nucleated heterogeneously on MSP cores. We compare the UM-UKCA results to new MSP-sulphuric simulations with the European stratosphere-troposphere chemistry-aerosol modelling system IFS-CB05-BASCOE-GLOMAP. The simulations show a strong seasonal cycle in meteoric-sulphuric particle abundance results from the winter-time source of MSPs transported down into the stratosphere in the polar vortex. Coagulation during downward transport sees high latitude MSP concentrations reduce from ~500 per cm3 at 40km to ~20 per cm3 at 25km, the uppermost extent of the stratospheric aerosol particle layer (the Junge layer). Once within the Junge layer’s supersaturated environment, meteoric-sulphuric particles form readily on the MSP cores, growing to 50-70nm dry-diameter (Dp) at 20-25km. Further inter-particle coagulation between these non-volatile particles reduces their number to 1-5 per cc at 15-20km, particle sizes there larger, at Dp ~100nm. The model predicts meteoric-sulphurics in high-latitude winter comprise >90% of Dp > 10nm particles above 25km, reducing to ~40% at 20km, and ~10% at 15km. These non-volatile particle fractions are slightly less than measured from high-altitude aircraft in the lowermost Arctic stratosphere (Curtius et al., 2005; Weigel et al., 2014), and consistent with mid-latitude aircraft measurements of lower stratospheric aerosol composition (Murphy et al., 1998), total particle concentrations also matching in-situ balloon measurements from Wyoming (Campbell and Deshler, 2014). The MSP-sulphuric interactions also improve agreement with SAGE-II observed stratospheric aerosol extinction in the quiescent 1998-2002 period. Simulations with a factor-8-elevated MSP input form more Dp>10nm meteoric-sulphurics, but the increased number sees fewer growing to Dp ~100nm, the increased MSPs reducing the stratospheric aerosol layer’s light extinction.

We have developed a new experimental system to study the pyrolysis of the refractory organic constituents in cosmic dust. Pyrolysis is observed by mass spectrometric detection of CO2 and SO2, and starts from around 850 K. The time-resolved kinetic behaviour is consistent with two organic components – one significantly more refractory than the other, which probably correspond to the insoluble and soluble organic fractions, respectively. The laboratory results are then incorporated into the Leeds Chemical Ablation Model (CABMOD), which is used to predict the conditions under which organic pyrolysis should be detectable using a high performance/large aperture radar. It has been proposed that loss of the organics leads to fragmentation of cometary dust particles into micron-sized fragments. If fragmentation of dust particles from Jupiter Family and Halley Type Comets does occur to a significant extent, there are several important implications: 1) slow-moving particles, particularly from Jupiter Family Comets, will be undetectable by radar, so that the total dust input to the atmosphere may be considerably larger than current estimates of 20 – 50 tonnes per day; 2) experiments at Leeds show that meteoritic fragments are excellent ice nuclei for freezing stratospheric droplets in the polar lower stratosphere, producing polar stratospheric clouds which activate chlorine and cause ozone depletion; and 3) the measured accumulation rates of meteoric smoke particles, micrometeorites and cosmic spherules in the polar regions can now be explained self-consistently.