The prevalence of meteoric-sulphuric particles within the stratospheric
aerosol layer
Abstract
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.