Spectral microphysics in weather forecast models
with special emphasis on cloud droplet nucleation

Idealized mountain overflow

Setup
The warm microphysics was tested with an idealized mountain overflow. A sensitivity study was performed with respect to mountain height using initial number concentrations of 100 cm^-3 respectively 1000 cm^-3.

• Initialization of atmosphere by idealized initial sounding after Thompson [1].
• Gauss shaped mountain, initial horizontal wind 15 m/s (from the "left").
• 400 gridpoints in horizontal direction, resolution 2.8 km.
• 38 vertical layers, model top 16 km, resolution about 50 m near ground up to 700 m near top.

Results

The resulting precipitation pattern from model runs with three different mountain heights and the two different initial aersosol particle number is shown to the left. The higher the mountain, the more rain results. Also, the peak maximum is shifted upwind. A more polluted atmosphere leads to less rain.
The total liquid water content (including rain) for the mountain height 1000 m is shown below. The left picture shows the result from the cleaner case, the right picture the result from the more polluted case. In the latter, most of the water is located in the cloud, while in the former most of the water is located near the ground as rain water.


References
[1] Thompson et al. (2004), Mon. Wea. Rev., 132, 519-542