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[MIS19-02] Analysis of Charge Separation Characteristics in Mixed-Phase Clouds Using RGB Hexagram
Keywords:cloud microphysics, charge separation, mixed-phase cloud, RGB hexagram
Charge separation due to riming electrification via collisions between solid particles in convective clouds is a primary charge separation process, which is governed by temperature and cloud water content[1]. Although the riming electrification process occurs in mixed-phase areas, the characteristics of mixed-phase areas suitable for charge separation remain insufficiently understood. To investigate these characteristics, this study conducted idealized simulations of an isolated deep convective cloud using the meteorological model; SCALE[2][3][4] coupled with a bulk lightning model, which explicitly calculates the riming electrification process. The mixed-phase areas were analyzed using an RGB hexagram[5], which allows diverse mixing properties to be represented, with liquid water, graupel, and snow assigned to RGB values.
The idealized simulations targeted a summertime deep convective cloud with the same initial conditions as Guo et al. (1999)[6]. A warm bubble, with a maximum temperature anomaly of 4.5 K above the domain-averaged temperature, was located at the center of the model domain. The calculation time and the output interval were 30 min, and 20 sec, respectively. The RGB values were defined with liquid water and graupel reaching maximum values of 15.6 g/m³ and snow reaching a maximum of 1.56 g/m³, represented on a 256-level scale. Furthermore, the vertical axis of the RGB hexagram was assigned to temperature, ranging from -70°C to 30°C.
The simulation results showed that at 19 min from the initial time, before the onset of precipitation, the graupel charge separation amount reached its peak with the peak number concentration of graupel particles exceeding 50 mg in average mass. The vertical cross-section at this time was visualized using the defined RGB values. The analysis of grid points corresponding to different RGB combinations in the RGB hexagram revealed that charge separation was most active in mixed-phase areas dominated by graupel and snow with small liquid water content. Furthermore, the temporal evolution of the charge separation area indicated that active charge separation areas corresponded to the areas with high snow number concentration within the temperature range of -20°C to -30°C. These characteristics suggest that the actively charging mixed-phase areas corresponded to the deposition in the dry growth regime in the riming electrification mechanism[7].
The idealized simulations targeted a summertime deep convective cloud with the same initial conditions as Guo et al. (1999)[6]. A warm bubble, with a maximum temperature anomaly of 4.5 K above the domain-averaged temperature, was located at the center of the model domain. The calculation time and the output interval were 30 min, and 20 sec, respectively. The RGB values were defined with liquid water and graupel reaching maximum values of 15.6 g/m³ and snow reaching a maximum of 1.56 g/m³, represented on a 256-level scale. Furthermore, the vertical axis of the RGB hexagram was assigned to temperature, ranging from -70°C to 30°C.
The simulation results showed that at 19 min from the initial time, before the onset of precipitation, the graupel charge separation amount reached its peak with the peak number concentration of graupel particles exceeding 50 mg in average mass. The vertical cross-section at this time was visualized using the defined RGB values. The analysis of grid points corresponding to different RGB combinations in the RGB hexagram revealed that charge separation was most active in mixed-phase areas dominated by graupel and snow with small liquid water content. Furthermore, the temporal evolution of the charge separation area indicated that active charge separation areas corresponded to the areas with high snow number concentration within the temperature range of -20°C to -30°C. These characteristics suggest that the actively charging mixed-phase areas corresponded to the deposition in the dry growth regime in the riming electrification mechanism[7].