Microphysical process comparison of three microphysics parameterization schemes in the WRF model for an idealized squall-line case study

Abstract

Three bulk microphysics schemes with different complexities in the Weather Research and ForecastingModel are compared in terms of the individual microphysical process terms of the hydrometeor mass andnumber mixing ratio tendency equations in an idealized 2D squall-line case. Through evaluation of theseprocess terms and of hydrometeor size distributions, it is shown that the differences in the simulated population characteristics of snow, graupel, and rainwater are the prominent factors contributing to the differences in the development of the simulated squall lines using these schemes. In this particular case, the gustfront propagation speed produced by the Thompson scheme is faster than in the other two schemes during thefirst 2 h of the simulation because it has a larger dominant graupel size. After 2 h into the simulation, theinitially less intense squall lines in the runs using the WSM6 and Morrison schemes start to catch up inintensity and development to the run using the Thompson scheme. Because the dominant size of graupelparticles in the runs using the WSM6 and Morrison schemes is smaller, these particles take more time to fallbelow the freezing level and enhance the rainwater production and its evaporative cooling. In the run usingthe Thompson scheme, the graupel production slows down at later times while the snow particle growthincreases, leading to more snow falling below the freezing level to melt and surpass graupel particle melting inthe production of rainwater.