Set the ice cloud asymmetry factor for all wavelengths and altitudes to a float between -1.0 and 1.0. Please note that this option is only applied if a Henyey-Greenstein phase function is used but not if an explicit phase function is defined e.g. with a ic_files. It doesn't make sense to modify only the first moment of an explicit phase function.  

ic_set_gg value

 
If you use this option in combination with the ice cloud properties by Fu1996, please make sure that you understand the explanation of ic_fu_tau.