def CT_to_class(CT):
    """
    Converts a CT layer from raw sea ice concentrations (0-100) to class ids (0-10).
    """
    
    CTs = list(range(0, 110, 10))
    class_ids = list(range(0, 11, 1))
    for i in range(len(CTs)):
        CT[CT == CTs[i]] = class_ids[i]
                   
    return CT