Abstract
Abstract. This study examines how different microphysical parameterization schemes influence orographically induced precipitation and the distributions of hydrometeors and water vapour for midlatitude summer conditions in the Weather Research and Forecasting (WRF) model. A high-resolution two-dimensional idealized simulation is used to assess the differences between the schemes in which a moist air flow is interacting with a bell-shaped 2 km high mountain. Periodic lateral boundary conditions are chosen to recirculate atmospheric water in the domain. It is found that the 13 selected microphysical schemes conserve the water in the model domain. The gain or loss of water is less than 0.81% over a simulation time interval of 61 days. The differences of the microphysical schemes in terms of the distributions of water vapour, hydrometeors and accumulated precipitation are presented and discussed. The Kessler scheme, the only scheme without ice-phase processes, shows final values of cloud liquid water 14 times greater than the other schemes. The differences among the other schemes are not as extreme, but still they differ up to 79% in water vapour, up to 10 times in hydrometeors and up to 64% in accumulated precipitation at the end of the simulation. The microphysical schemes also differ in the surface evaporation rate. The WRF single-moment 3-class scheme has the highest surface evaporation rate compensated by the highest precipitation rate. The different distributions of hydrometeors and water vapour of the microphysical schemes induce differences up to 49 W m−2 in the downwelling shortwave radiation and up to 33 W m−2 in the downwelling longwave radiation.
Highlights
Atmospheric processes that occur at spatial and temporal scales not resolved by global and regional climate models (GCMs and RCMs) are represented by means of physical parameterizations based on several assumptions and approximations
This study focuses on the microphysical schemes, the parameterizations responsible for computing atmospheric water vapour, cloud liquid water, cloud ice and various types of precipitation
Our study investigates the effects of the 13 microphysical schemes available in Weather Research and Forecasting (WRF) v3.3.1 on orographic precipitation and on the atmospheric water cycle by performing a simple idealized simulation running over a period of two months
Summary
Atmospheric processes that occur at spatial and temporal scales not resolved by global and regional climate models (GCMs and RCMs) are represented by means of physical parameterizations (or schemes) based on several assumptions and approximations. The lack of a study which considers more microphysical schemes at the same time and assesses them using a simple scenario has motivated us to perform an idealized simulation with a fixed set of physical schemes and a simple terrain model. This method prevents a direct verification with observations and forces the microphysics to interact with a limited number of other physical schemes, it still provides useful information about the range of results that can be obtained using different microphysical schemes. At the beginning of the Runge–Kutta time step, the radiation, surface and planetary boundary layer schemes produce tendencies of atmospheric state variables, while the microphysics, being an adjustment process, does not provide tendencies but updates the atmospheric state only at the end of the model time step
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