AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Initiation of Secondary Ice Production in Clouds
Sylvia Sullivan, Corinna Hoose, Alexei Kiselev, Thomas Leisner, ATHANASIOS NENES, Georgia Institute of Technology
Abstract Number: 493 Working Group: Aerosols, Clouds, and Climate
Abstract Disparities between the measured concentrations of ice-nucleating particles (INP) and in-cloud ice crystal number concentrations (ICNC) have led to the hypothesis that mechanisms other than primary nucleation form ice in the atmosphere. In this work, we model three such secondary production mechanisms -- rime splintering, frozen droplet shattering, and breakup upon collision -- with a six-hydrometeor-class parcel model. We quantify the ICNC enhancement magnitude and timing from all processes for a range of thermodynamic conditions and parameter values. We also calculate the number of primarily nucleated ice crystals that must exist before secondary ice production initiates, denoted NINP(lim). This value is particularly relevant to bioaerosol: if biological INP are present at concentrations greater than NINP(lim), they may be sufficient to generate large concentrations of cloud ice. Our simulations indicate that breakup upon collision is the only process for which a meaningful NINP(lim) exists (0.002 L-1 up to 0.07 L-1). For droplet shattering and rime splintering, a warm enough cloud base temperature and modest updraft are the more important criteria for initiation. Low, simulated values of NINP(lim) suggest that, under appropriate thermodynamic conditions for secondary ice production, perturbations in CCN concentrations are more influential on cloud phase partitioning than those in INP concentrations.