The NASA Ames legacy Mars global climate model: Radiation code error correction and new baseline water cycle simulation

Haberle et al. (2019) documented the status of the NASA Ames Legacy Mars Global Climate Model (GCM) and presented a baseline water cycle simulation. Since publishing that manuscript, we have found an error in the Legacy Mars GCM radiation code related to how the infrared cloud opacities were computed. Here we document this code error, its correction, how the corrected radiation code affects the simulated water cycle from Haberle et al. (2019), and what is required to produce a new realistic baseline water cycle simulation. We show that we can recover many, but not all, of the key aspects of the Haberle et al. (2019) baseline simulation by implementing a small change to the contact parameter, which is a microphysical parameter that affects the ease at which nucleation occurs. The fact that such a small change to the contact parameter can yield very different water cycles illustrates how sensitive the climate system is to cloud microphysical processes and highlights the need for future numerical and experimental study.