def get_rad4alp_grid_dir(basepath, voltime, datatype, acronym,
    path_convention='MCH'):
    """
    gets the directory where rad4alp grid data is stored

    Parameters
    ----------
    basepath : str
        base path
    voltime : datetime object
        nominal time
    datatype : str
        data type
    acronym : str
        acronym identifying the data type
    path_convention : str
        The path convention. Can be 'LTE', 'MCH' or 'RT'

    Returns
    -------
    datapath : str
        The data path

    """
    nowpal_accu = ('nowpal60_P60', 'nowpal90_P90', 'nowpal180_P180',
        'nowpal360_P360', 'nowpal720_P720')
    nowpal = ('nowpal90_P30', 'nowpal90_P30_F60', 'nowpal90_F60',
        'nowpal180_P60', 'nowpal180_P60_F120', 'nowpal180_F120',
        'nowpal360_P120', 'nowpal360_P120_F240', 'nowpal360_F240',
        'nowpal720_P360', 'nowpal720_P360_F360', 'nowpal720_F360')
    cpch = ('CPCH0005', 'CPCH0060', 'CPCH0180', 'CPCH0360', 'CPCH0720',
        'CPCH1440', 'CPCH2880', 'CPCH4320')
    dayinfo = voltime.strftime('%y%j')
    if datatype in nowpal_accu:
        dirbase = 'nowpal_accu'
    elif datatype in nowpal:
        dirbase = 'nowpal'
    elif datatype.startswith('d') and datatype != 'dGZC':
        dirbase = 'd' + acronym
        if datatype.endswith('H'):
            dirbase = dirbase + 'H'
    elif datatype in cpch:
        dirbase = acronym + 'H'
    else:
        dirbase = acronym
    if path_convention == 'LTE':
        yy = dayinfo[0:2]
        dy = dayinfo[2:]
        subf = acronym + yy + 'hdf' + dy
        datapath = basepath + subf + '/'
    elif path_convention == 'MCH':
        datapath = basepath + dayinfo + '/' + dirbase + dayinfo + '/'
    else:
        datapath = basepath + dirbase + '/'
    return datapath
