“…Tephra2 is a widely-used volcanic ash transport and deposition model (Bonadonna et al, 2010;Connor et al, 2011). It has been coupled with different statistical and engineering techniques for forward and inverse modeling of tephra fall deposits and volcanic hazard analysis (Connor and Connor, 2006;Mannen, 2006;Volentik et al, 2010;Fontijn et al, 2011;Biass et al, 2012;Mannen, 2014;Magill et al, 2015;Biass et al, 2016Biass et al, , 2017Takarada, 2017;Wild et al, 2019;Connor et al, 2019;Mannen et al, 2020;Williams et al, 2020). Tephra2 assumes that tephra particles with different grain sizes are released from a vertical column with column radius increasing with height (accounted for by an additional diffusion term; Suzuki et al, 1983), and their transport is subject to wind advection, horizontal turbulent diffusion, and falling at terminal velocities.…”