Motivation Sensitivity of Precipitation to Aerosol Concentration. (Based partly on 2 d results). Theory: Precipitation occurring in a “maritime” airmass should develop sooner and precipitate on the upwind slope. Precipitation in continental aerosols should be displaced downwind (if it develops at all). Cloud tops in continental runs should be cooler, as slower diffusional growth is favored over growth processes occurring through collisions.

Set-Up First set of simulations was done with liquid only microphysical processes. Grid spacing was 3 km.

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Perhaps We need a source of aerosols to replace those scavenged. Simulation redone with constant (source of), continental aerosols.

Scavenging of aerosols leads to lower clouds with warmer cloud top temperatures (but dynamics more important). Figure 13

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Model Restarted Simulations with maritime and continental aerosols, starting from the same initial conditions at 16 GMT

Ice processes Figure 17 Some enhance ment of precip.

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Summary Part II: Initially, deep clouds over a mountainous terrain in a maritime environment produce more rain than clouds in a continental environment. Over time, the clouds in a continental environment produce more rain.

Explanation? Scavenging of large aerosols allows continental air mass to evolve towards a maritime condition. Differences in cloud height support this. Yet, even with constant aerosols in a continental environment, precipitation from clouds in this environment is more than in the maritime/continental simulation

Shallow clouds (should) conform to theory? Differences in precipitation from shallow clouds developed much the same way as deep clouds (but effect was proportionally more important). Cloud top heights were cooler in maritime simulation than in continental simulation? Including ice processes does not change the result. “Real world” is more complex than prevailing theory and results from 2d simulations.

Ongoing and Future Work Coupling of SBM in WRF (NSF SGER) Further investigation of aerosol effects on precipitation (PIER, Israeli Science Foundation, ANTISTORM) Development of hybrid SBM bulk microphysical model (?)