Therefore, the following dust updates proposed for V2 will address these the above three issues identified. First, we will update the dust refractive index in the SW with the AERONET (obs)-derived values from the OPAC data (Hess, 1998) that is used in the default configuration. Second, we will update the fractional dust emission fluxes in accumulation and coarse modes, calculated with the size distribution by Kok (2011). With these updates implemented, dust emissions need to be re-tuned for the globally constrained AOD.

To fundamentally address the over-deposition bias in dust, it requires some surgical change in the code - the aerosol turbulence transport term needs to be moved from CLUBB and add to the aerosol emission/deposition equation. This issue might also need affect other aerosols and water vapor, which probably requires extensive model evaluation. In view of the timeline for the V2, a simple fix is thus proposed. We will implement an alternative option that distribute dust evenly in the PBL, instead of the lowest model layer. As insufficient dust transport is common in large-scale models for various reasons, similar approaches have been adopted in other modeling studies to enhance the dust vertical transport. We propose to implement this simple fix as an option in the namelist so that we will have a short-term solution, while we are working on a more physically-based solution.