The reference paper of MicroHH is available as a discussion paper on the website of Geoscientific Model Development. This paper describes the final result of several years of model development: MicroHH 1.0.
The short summary on the GMD page describes the code as:
"MicroHH (www.microhh.org) is a new and open source computational fluid dynamics code for the simulation of turbulent flows in the atmosphere. It is made to simulate atmospheric flows up to the finest detail levels at very high resolution. It has been designed from scratch in order to use a modern design that allows the code to run on more than 10.000 cores, as well as on a Graphical Processing Unit."
van Heerwaarden, C.C. , van Stratum, B.J.H., Heus, T., Gibbs, J.A., Fedorovich, E., and Mellado, J.-P., 2017. MicroHH 1.0: a computational fluid dynamics code for direct numerical simulation and large-eddy simulation of atmospheric boundary layer flows, Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2017-41.