Global simulations using a subcolumn sampler for microphysics, SILHS

 

Author

Vincent Larson — University of Wisconsin, Milwaukee

Category

General topics – Clouds

Description

Small-scale variability in hydrometeors influences the evolution of cloud properties. For instance, rain that removes moisture from the moistest part of the cloud reduces variability in moisture over the cloud. It has been challenging to consistently represent such effects in global models. Here the effects are represented by the aid of sub-columns drawn from sub-grid distributions of hydrometeors. A microphysical tendency is computed on each sub-column, and the tendencies are averaged to form a grid-box average. The tendencies are applied not only to grid means, but also to variances and co-variances of cloud-related variables (Griffin and Larson 2016), thereby representing microphysical effects such as the one described above. Global simulations using sub-columns produce similar time-averaged precipitation fields at horizontal grid spacings of 25 km and 100 km. This suggests that the grid-scale sensitivity of the method is minor.