An Explicit Microphysical and Electrical Charging Model to Study the Effects of Changing Aerosol Composition on the Electric Field and Lightning Distribution

As climate changes, so will likely the aerosol composition of the atmosphere, possibly leading to substantial changes in cloud-aerosol interactions and associated charging of the atmosphere (including lightning intensity). A bin microphysical model is ideally suited to study such possible interactions. For these purposes, the aerosol distribution of the Hebrew University Cloud Model (HUCM) was altered to take into account desert dust and urban aerosols on nucleation. The microphysics part of the model, also known as Spectral (bin) Microphysics (SBM), has been coupled to the Weather Research and Forecasting Model (WRF). Additionally, SBM (in WRF) was coupled bin by bin to explicitly account for charging during collisions between small ice and large ice particles in the presence of supercooled liquid water. The model accounts for collisions between charged hydrometeors, break-up of charged particles, their advection and sedimentation. The electrical solver of WRF-ELEC is used to compute the electric field from bulk (integrated) charge concentrations within each grid point. A build up of the electric field can lead to the dissipation of the electric field through lightning discharges (cloud to ground and intracloud). The energy of the discharges is also calculated. Because droplet and ice concentrations depend on background aerosol conditions, the coupled model accounts for the effect of changes in aerosol composition on electrical charge distribution and resultant lightning. The model was used to simulate a US continental real-case squall-line and eastern Mediterranean storm where a large number of superbolts occurred. Results are described and compared to those obtained with the WRF-ELEC with bulk microphysics.